Working machine

ABSTRACT

In a working machine, a controller decreases a supply amount of hydraulic fluid from a travel pump to a travel motor based on a travel state of a machine body when a speed-change instruction is issued by operating a switch. When a speed-increase operation is performed, the controller switches the travel switching valve from the first state to the second state in a prior period lasting up to when the supply amount to the travel motor starts decreasing, in a restoration period in which the supply amount to the travel motor after being decreased is being restored, or in an after-restoration period in which the supply amount has been restored.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to Japanese PatentApplication No. 2021-205375 filed on Dec. 17, 2021. The entire contentsof this application are hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a working machine, such as a skid-steerloader, a compact track loader, or a backhoe.

2. Description of the Related Art

To date, a technology that decreases and increases the speed of aworking machine is disclosed in Japanese Unexamined Patent ApplicationPublication No. 2017-179922. The working machine disclosed in JapaneseUnexamined Patent Application Publication No. 2017-179922 above includesa prime mover, a hydraulic pump that operates by the operation of theprime mover and delivers a hydraulic fluid, a hydraulic switching valvethat is switchable to a plurality of switching positions in accordancewith the pressure of the hydraulic fluid, a proportional valve that iscapable of changing a hydraulic fluid that acts on the hydraulicswitching valve, a travel hydraulic device that is capable of changingthe speed in accordance with the switching position of the hydraulicswitching valve, and a controller that controls the proportional valvein accordance with, for example, a travel state of the working machineor a state of the prime mover.

SUMMARY OF THE INVENTION

In the working machine disclosed in Japanese Unexamined PatentApplication Publication No. 2017-179922 above, when changing the speed,that is, when decreasing the speed of the working machine, in order tochange the pressure characteristics of the switching of the hydraulicswitching valve, measures are taken to reduce a speed-change shock(impact or a sense of discomfort). However, in a working machine inwhich there is a shift in a speed-change timing resulting fromvariations in a delay in responding to the rotation of hydraulicequipment or the prime mover, the speed-change shock may not be reduced.

The present invention has been made to solve the problems of the relatedart as those described above, and an object of the present invention isto provide a working machine that is capable of suitably reducing aspeed-change shock.

Technical means that have been adopted by the present invention forsolving the technical problems are as follows.

A working machine according to an aspect of the present inventionincludes a prime mover; a travel pump driven by power of the prime moverto deliver a hydraulic fluid; a travel motor rotated by the hydraulicfluid delivered by the travel pump; a machine body where the primemover, the travel pump, and the travel motor are provided; a travelswitching valve switchable to a first state in which a rotation speed ofthe travel motor is capable of being increased up to a first maximumspeed, and to a second state in which the rotation speed of the travelmotor is capable of being increased up to a second maximum speed that isgreater than the first maximum speed; a travel operation deviceincluding an operation valve operable to change a pressure of ahydraulic fluid to operate the travel pump in accordance with anoperation of an operation member; and a controller configured orprogrammed to decrease a supply amount of the hydraulic fluid from thetravel pump to the travel motor based on a travel state of the machinebody when performing either one of a speed-increase operation ofswitching the travel switching valve from the first state to the secondstate and a speed-decrease operation of switching from the second stateto the first state. When the speed-increase operation is performed, thecontroller switches the travel switching valve from the first state tothe second state in a prior period lasting up to when the supply amountto the travel motor starts decreasing, in a restoration period in whichthe supply amount to the travel motor after being decreased is beingrestored, or in an after-restoration period in which the supply amountto the travel motor has been restored.

A working machine according to an aspect of the present inventionincludes a prime mover; a travel pump driven by power of the prime moverto deliver a hydraulic fluid; a travel motor rotated by the hydraulicfluid delivered by the travel pump; a machine body where the primemover, the travel pump, and the travel motor are provided; a travelswitching valve switchable to a first state in which a rotation speed ofthe travel motor is capable of being increased up to a first maximumspeed, and to a second state in which the rotation speed of the travelmotor is capable of being increased up to a second maximum speed that isgreater than the first maximum speed; a travel operation deviceincluding an operation valve operable to change a pressure of ahydraulic fluid to operate the travel pump in accordance with anoperation of an operation member; and a controller configured orprogrammed to decrease a supply amount of the hydraulic fluid from thetravel pump to the travel motor based on a travel state of the machinebody when performing either one of a speed-increase operation ofswitching the travel switching valve from the first state to the secondstate and a speed-decrease operation of switching the travel switchingvalve from the second state to the first state. When the speed-decreaseoperation is performed, the controller switches the travel switchingvalve from the second state to the first state in a prior period lastingup to when the supply amount to the travel motor starts decreasing, in adecrease period in which the supply amount to the travel motor is beingdecreased, or in an after-restoration period in which the supply amountof the travel motor after being decreased has been restored.

In the working machine of an aspect of the present invention, when thespeed-decrease operation is performed, the controller may switch thetravel switching valve from the second state to the first state in theprior period lasting up to when the supply amount to the travel motorstarts decreasing, in a decrease period in which the supply amount tothe travel motor is being decreased, or in the after-restoration periodin which the supply amount of the travel motor after being decreased hasbeen restored.

The working machine according to an aspect of the present invention mayfurther include a travel detector to detect a travel speed of themachine body as the travel state. When the speed-increase operation isperformed, the controller may determine a decrease amount of the supplyamount to the travel motor corresponding to the travel speed detected bythe travel detector, and may decrease the supply amount to the travelmotor in accordance with the decrease amount that has been determined.

The working machine according to an aspect of the present invention mayfurther include a travel detector to detect a travel speed of themachine body as the travel state. When the speed-decrease operation isperformed, the controller may determine a decrease amount of the supplyamount to the travel motor corresponding to the travel speed detected bythe travel detector, and may decrease the supply amount to the travelmotor in accordance with the decrease amount that has been determined.

The working machine according to an aspect of the present invention mayfurther include a switch operable to issue a speed-change instruction ofeither increasing or decreasing speed; and an accelerator operable todetermine a rotation speed of the prime mover. The controller maydecrease the supply amount of the hydraulic fluid from the travel pumpto the travel motor by decreasing the rotation speed of the prime mover.When the speed-change instruction of increasing the speed is issued byoperating the switch, the controller may switch the travel switchingvalve from the first state to the second state in accordance with thespeed-change instruction in a prior period lasting up to when therotation speed of the prime mover starts decreasing, in a restorationperiod in which the rotation speed of the prime mover after beingdecreased to a value lower than a target rotation speed that is therotation speed of the prime mover determined by operating theaccelerator is being restored, or in an after-restoration period inwhich the rotation speed of the prime mover has been restored.

The working machine according to an aspect of the present invention mayfurther include a switch operable to issue a speed-change instruction ofeither increasing or decreasing speed; and an accelerator operable todetermine a rotation speed of the prime mover. The controller maydecrease the supply amount of the hydraulic fluid from the travel pumpto the travel motor by decreasing the rotation speed of the prime mover.When the speed-change instruction of decreasing the speed is issued byoperating the switch, the controller may switch the travel switchingvalve from the second state to the first state in accordance with thespeed-change instruction in a prior period lasting up to when therotation speed of the prime mover starts decreasing, in a decreaseperiod in which the rotation speed of the prime mover is being decreasedto a value lower than a target rotation speed that is the rotation speedof the prime mover determined by operating the accelerator, or in anafter-restoration period in which the rotation speed of the prime moverafter being decreased to the value has been restored.

In working machine according to an aspect of the present invention, whenthe speed-change instruction of decreasing the speed is issued byoperating the switch, the controller may switch the travel switchingvalve from the second state to the first state in accordance with thespeed-change instruction in the prior period lasting up to when therotation speed of the prime mover starts decreasing, in a decreaseperiod in which the rotation speed of the prime mover is being decreasedto a value lower than the target rotation speed determined by operatingthe accelerator, or in the after-restoration period in which therotation speed of the prime mover after being decreased to the value hasbeen restored.

The working machine according to an aspect of the present invention mayfurther include a switch operable to issue a speed-change instruction ofeither increasing or decreasing speed; and an actuating valve connectedto the operation valve on an upstream side or a downstream side of theoperation valve and operable to control a hydraulic fluid that flows inthe operation valve. When the speed-change instruction of increasing thespeed is issued by operating the switch, the controller may switch thetravel switching valve from the first state to the second state inaccordance with the speed-change instruction in a prior period lastingup to when an opening of the actuating valve starts decreasing, in arestoration period in which the opening of the actuating valve afterbeing decreased is being restored, or in an after-restoration period inwhich the opening of the actuating valve after being decreased has beenrestored.

The working machine according to an aspect of the present invention mayfurther include a switch operable to issue a speed-change instruction ofeither increasing or decreasing speed; and an actuating valve connectedto the operation valve on an upstream side or a downstream side of theoperation valve and that is capable of controlling a hydraulic fluidthat flows in the operation valve. When the speed-change instruction ofdecreasing the speed is issued by operating the switch, the controllermay switch the travel switching valve from the second state to the firststate in accordance with the speed-change instruction in a prior periodlasting up to when an opening of the actuating valve starts decreasing,in a decrease period in which the opening of the actuating valve isbeing decreased, or in an after-restoration period in which the openingof the actuating valve after being decreased has been restored.

In the working machine according to an aspect of the present invention,when the speed-change instruction of decreasing the speed is issued byoperating the switch, the controller may switch the travel switchingvalve from the second state to the first state in accordance with thespeed-change instruction in the prior period lasting up to when theopening of the actuating valve starts decreasing, in a decrease periodin which the opening of the actuating valve is being decreased, or inthe after-restoration period in which the opening of the actuating valveafter being decreased has been restored.

The working machine according to an aspect of the present invention mayfurther include a switch operable to issue a speed-change instruction ofeither increasing or decreasing speed; an accelerator operable todetermine a rotation speed of the prime mover;

and an actuating valve connected to the operation valve on an upstreamside or a downstream side of the operation valve and operable to controla hydraulic fluid that flows in the operation valve. When thespeed-change instruction of increasing the speed is issued by operatingthe switch, the controller may switch the travel switching valve fromthe first state to the second state in accordance with the speed-changeinstruction in a prior period lasting up to when an opening of theactuating valve starts decreasing, in a restoration period in which theopening of the actuating valve after being decreased is being restored,or in an after-restoration period in which the opening of the actuatingvalve has been restored. When the speed-change instruction of decreasingthe speed is issued by operating thee switch, the controller may switchthe travel switching valve from the second state to the first state inaccordance with the speed-change instruction in a prior period lastingup to when a rotation speed of the prime mover starts decreasing, in adecrease period in which the rotation speed of the prime mover isdecreased to a value lower than a target rotation speed that is therotation speed of the prime mover determined by operating theaccelerator, or in an after-restoration period in which the rotationspeed of the prime mover after being decreased to the value has beenrestored.

In the working machine according to an aspect of the present invention,the switch may be a switch to output the speed-change instruction to thecontroller.

In the working machine according to an aspect of the present invention,when the speed-increase operation is performed, the controller may causean absolute value of a gradient of a supply amount to the operationvalve in the restoration period to be smaller than that in a decreaseperiod in which the supply amount to the travel motor is beingdecreased.

In the working machine according to an aspect of the present invention,when the speed-decrease operation is performed, the controller may causean absolute value of a gradient of a supply amount to the operationvalve in the decrease period to be smaller than that in the restorationperiod.

The above and other elements, features, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of the preferred embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of preferred embodiments of the presentinvention and many of the attendant advantages thereof will be readilyobtained as the same becomes better understood by reference to thefollowing detailed description when considered in connection with theaccompanying drawings described below.

FIG. 1 illustrates a hydraulic system (hydraulic circuit) of a workingmachine in a first embodiment.

FIG. 2A illustrates the relationship between the rotation speed of aprime mover when the speed of a travel motor is increased, and switchingof the travel motor.

FIG. 2B illustrates the relationship between the rotation speed of theprime mover when the speed of the travel motor is decreased, and theswitching of the travel motor.

FIG. 2C illustrates an example of a memory table.

FIG. 2D is a graph showing a change in a delay period on the basis of aforward-movement travel pressure and a rearward-movement travelpressure.

FIG. 2E illustrates the relationship between the rotation speed of theprime mover when the speed of the travel motor is increased, and theswitching of the travel motor.

FIG. 2F illustrates the relationship between the rotation speed of theprime mover when the speed of the travel motor is decreased, and theswitching of the travel motor.

FIG. 2G illustrates the relationship between the rotation speed of theprime mover when the speed of the travel motor is increased, and theswitching of the travel motor.

FIG. 2H illustrates the relationship between the rotation speed of theprime mover when the speed of the travel motor is decreased, and theswitching of the travel motor.

FIG. 3A is a flowchart of a first operation of a controller when thespeed of the travel motor is increased.

FIG. 3B is a flowchart of a second operation of the controller when thespeed of the travel motor is decreased.

FIG. 3C is a flowchart of an operation of changing a speed-changeswitching delay period of the controller at the time of aforward-movement speed-increase.

FIG. 3D is a flowchart of an operation of changing the speed-changeswitching delay period of the controller at the time of aforward-movement speed-decrease.

FIG. 3E is a flowchart of an operation of changing a speed-changeswitching delay period of a controller at the time of a forward-movementspeed-increase in a second embodiment.

FIG. 3F is a flowchart of an operation of changing the speed-changeswitching delay period of the controller at the time of aforward-movement speed-decrease in the second embodiment.

FIG. 4A illustrates the relationship between a swash-plate angle of atravel pump when the speed of a travel motor is increased, and switchingof the travel motor.

FIG. 4B illustrates the relationship between the swash-plate angle ofthe travel pump when the speed of the travel motor is decreased, and theswitching of the travel motor.

FIG. 4C illustrates the relationship between the swash-plate angle of atravel pump when the speed of a travel motor is increased, and switchingof the travel motor.

FIG. 4D illustrates the relationship between the swash-plate angle ofthe travel pump when the speed of the travel motor is decreased, and theswitching of the travel motor.

FIG. 4E illustrates the relationship between the swash-plate angle ofthe travel pump when the speed of the travel motor is increased, and theswitching of the travel motor.

FIG. 4F illustrates the relationship between the swash-plate angle ofthe travel pump when the speed of the travel motor is decreased, and theswitching of the travel motor.

FIG. 5A is a flowchart of a third operation of a controller when thespeed of a travel motor is increased.

FIG. 5B is a flowchart of a fourth operation of the controller when thespeed of the travel motor is decreased.

FIG. 6A illustrates a hydraulic system (hydraulic circuit) of a workingmachine in a third embodiment.

FIG. 6B illustrates part of a hydraulic system (hydraulic circuit) of aworking machine in Modification 4.

FIG. 6C illustrates part of a hydraulic system (hydraulic circuit) of aworking machine in Modification 5.

FIG. 7A illustrates a hydraulic system (hydraulic circuit) of a workingmachine in a fourth embodiment.

FIG. 7B illustrates a hydraulic system (hydraulic circuit) of a workingmachine in a fifth embodiment.

FIG. 8A is a table showing the relationship between an actual rotationspeed of a prime mover, a travel pilot pressure, and a decrease amountof the rotation speed of the prime mover.

FIG. 8B is a graph of FIG. 8A.

FIG. 9A is a table showing the relationship between a travel pilotpressure and a decrease amount of the travel pilot pressure.

FIG. 9B is a graph of FIG. 9A.

FIG. 10 is a side view of a track loader, which is an example of aworking machine.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments will now be described with reference to theaccompanying drawings, wherein like reference numerals designatecorresponding or identical elements throughout the various drawings. Thedrawings are to be viewed in an orientation in which the referencenumerals are viewed correctly.

Preferred embodiments of a hydraulic system of a working machine and aworking machine including the hydraulic system according to the presentinvention are described below with reference to the drawings asappropriate.

First Embodiment

FIG. 10 is a side view of a working machine 1 according to the presentinvention. FIG. 10 illustrates a compact track loader as an example ofthe working machine 1.

However, the working machine according to the present invention is notlimited to a compact track loader, and may be, for example, another typeof loader working machine, such as a skid-steer loader. Alternatively,the working machine may be a working machine other than a loader workingmachine.

As shown in FIG. 10 , the working machine 1 includes a machine body 2, acabin 3, a working device 4, and at least one traveling device 5. In thefirst embodiment of the present invention, a direction that an operatorseated on an operator's seat 8 of the working machine 1 faces (left sidein FIG. 10 ) is a forward direction, and the opposite direction (rightside in FIG. 10 ) is a rearward direction. A left side of the operator(near side in FIG. 10 ) is a leftward direction, and a right side of theoperator (far side in FIG. 10 ) is a rightward direction. Note that ahorizontal direction that is a direction orthogonal to a front-reardirection is a machine-body width direction, and a direction from acentral portion of the machine body 2 toward a right portion or a leftportion thereof is a machine-body outward direction. In other words, themachine-body outward direction is a machine-body width direction and adirection away from the machine body 2. A direction opposite to themachine-body outward direction is a machine-body inward direction. Inother words, the machine-body inward direction is a machine-body widthdirection and a direction toward the machine body 2.

The cabin 3 is installed on the machine body 2. The operator's seat 8 isprovided at the cabin 3. The working device 4 is mounted on the machinebody 2. The at least one traveling device 5 is provided on an outer sideof the machine body 2. A prime mover 32 is installed at a rear portioninside the machine body 2.

The working device 4 has at least one boom 10, a bucket 11, which is anexample of a working tool, at least one lift link 12, at least onecontrol link 13, at least one boom cylinder 14, and at least one bucketcylinder 15.

The at least one boom 10 includes booms 10 that are provided, one on theright side and the other on the left side of the cabin 3. The bucket 11is provided on an end portion (front end portion) of each boom 10 so asto be swingable upward and downward. The at least one lift link 12 andthe at least one control link 13 support a base portion (rear portion)of each boom 10 so that each boom 10 is swingable upward and downward.The at least one boom cylinder 14 extends and contracts to raise andlower the booms 10. The at least one bucket cylinder 15 extends andcontracts to swing the bucket 11.

The front end portion of the left boom 10 and the front end portion ofthe right boom 10 are connected to each other by an oddly shapedconnection pipe. The base portions (rear portions) of the respectivebooms 10 are connected to each other by a circular connection pipe.

The at least one lift link 12 includes lift links 12, the at least onecontrol link 13 includes control links 13, and the at least one boomcylinder 14 includes boom cylinders 14. The lift links 12, the controllinks 13, and the boom cylinders 14 are provided on a corresponding oneof the left side and the right side of the machine body 2 incorrespondence with a corresponding one of the left boom 10 and theright boom 10.

The lift links 12 are provided vertically on a rear portion of the baseportion of a corresponding one of the booms 10. An upper portion (oneend) of each lift link 12 is pivotally supported so as to be rotatablearound a lateral axis via a pivoted shaft (for example, a first pivotedshaft 16) situated toward the rear portion of the base portion of eachboom 10. A lower portion (the other end) of each lift link 12 ispivotally supported so as to be rotatable around a lateral axis via apivoted shaft (for example, a second pivoted shaft 17) situated towardthe rear portion of the machine body 2. The second pivoted shaft 17 isprovided below the first pivoted shaft 16.

An upper portion of each boom cylinder 14 is pivotally supported so asto be rotatable around a lateral axis via a pivoted shaft (for example,a third pivoted shaft 18). The third pivoted shaft 18 is the baseportion of each boom 10, and is provided at a front portion of the baseportion. A lower portion of each boom cylinder 14 is pivotally supportedso as to be rotatable around a lateral axis via a pivoted shaft (forexample, a fourth pivoted shaft 19). The fourth pivoted shaft 19 isprovided toward a lower portion of the rear portion of the machine body2 and below the third pivoted shaft 18.

The control links 13 are provided forward of the lift links 12. One endof each control link 13 is pivotally supported so as to be rotatablearound a lateral axis via a pivoted shaft (for example, a fifth pivotedshaft 20). The fifth pivoted shaft 20 is provided at a position, forwardof the lift links 12, on the machine body 2. The other end of eachcontrol link 13 is pivotally supported so as to be rotatable around alateral axis via a pivoted shaft (for example, a sixth pivoted shaft21). The sixth pivoted shaft 21 is provided on each boom 10 so as to besituated forward of the second pivoted shaft 17 and above the secondpivoted shaft 17.

Due to extension and contraction of the boom cylinders 14, while thebase portions of the booms 10 are supported by the lift links 12 and thecontrol links 13, the booms 10 swing upward and downward around thefirst pivoted shaft 16, and the end portions of the booms 10 are raisedand lowered. The control links 13 swing upward and downward around thefifth pivoted shaft 20 as the booms 10 swing upward and downward. Thelift links 12 swing forward and rearward around the second pivoted shaft17 as the control links 13 swing upward and downward.

Instead of the bucket 11, a different working tool can be mounted on afront portion of each boom 10. As a different working tool, there existsan attachment (auxiliary attachment) of, for example, a hydrauliccrusher, a hydraulic breaker, an angle broom, an earth auger, a palletfork, a sweeper, a mower, or a snow blower.

A connecting member 50 is provided on a front end of the left boom 10.The connecting member 50 is a device that connects hydraulic equipmentthat is provided at the auxiliary attachment and a first tubularmaterial, such as a pipe, that is provided at each boom 10 to eachother. Specifically, the first tubular material is connectable to oneend of the connecting member 50, and a second tubular material that isconnected to the hydraulic equipment of the auxiliary attachment isconnectable to the other end of the connecting member 50. Therefore, ahydraulic fluid that flows in the first tubular material passes throughthe second tubular material and is supplied to the hydraulic equipment.

The at least one bucket cylinder 15 includes bucket cylinders 15 thatare each disposed toward the front portion of a corresponding one of thebooms 10. Due to extension and contraction of each bucket cylinder 15,the bucket 11 is swung.

The at least one traveling device 5 includes left and right travelingdevices (a first traveling device and a second traveling device) 5, and,in the embodiment, crawler (including semicrawler) traveling devices areused. Note that wheeled traveling devices having a front wheel and arear wheel may be used.

The prime mover 32 is, for example, an internal combustion engine, suchas a diesel engine or a gasoline engine, or an electric motor. Although,in the embodiment, the prime mover 32 is a diesel engine, the primemover 32 is not limited thereto.

Next, a hydraulic system of the working machine 1 is described.

As shown in FIG. 1 , the hydraulic system of the working machine 1 iscapable of driving the traveling devices 5. The hydraulic system of theworking machine 1 includes a first travel pump 53L, a second travel pump53R, a first travel motor 36L, and a second travel motor 36R.

The first travel pump 53L and the second travel pump 53R are pumps thatare driven by power of the prime mover 32. Specifically, the firsttravel pump 53L and the second travel pump 53R are swash-plate variabledisplacement axial pumps that are driven by the power of the prime mover32. The first travel pump 53L and the second travel pump 53R each have aforward-movement pressure receiver 53 a and a rearward-movement pressurereceiver 53 b upon which pilot pressure acts. The swash-plate angles ofthe first travel pump 53L and the second travel pump 53R are eachchanged by the pilot pressure that acts upon the forward-movementpressure receiver 53 a and the rearward-movement pressure receiver 53 b.Outputs of the first travel pump 53L and the second travel pump 53R(delivery amounts of hydraulic fluid) and delivery directions of thehydraulic fluid can be changed by changing the swash-plate angles.

The first travel pump 53L and the first travel motor 36L are connectedto each other by a circulation fluid passage 57 h, and a hydraulic fluiddelivered from the first travel pump 53L is supplied to the first travelmotor 36L. The second travel pump 53R and the second travel motor 36Rare connected to each other by a circulation fluid passage 57 i, and ahydraulic fluid delivered from the second travel pump 53R is supplied tothe second travel motor 36R.

The first travel motor 36L is a motor that transmits power to a driveshaft of the traveling device 5 provided on the left side of the machinebody 2. The first travel motor 36L is rotatable by the hydraulic fluiddelivered from the first travel pump 53L, and its rotation speed can bechanged by the flow rate of the hydraulic fluid. A swash-plate switchingcylinder 37L is connected to the first travel motor 36L, and therotation speed of the first travel motor 36L can be changed even byextending and contracting the swash-plate switching cylinder 37L in onedirection or in the other direction. That is, when the swash-plateswitching cylinder 37L is contracted, the rotation speed of the firsttravel motor 36L is set at a low speed (a first speed region up to afirst maximum speed; hereunder abbreviated as “first speed” asappropriate), and, when the swash-plate switching cylinder 37L isextended, the rotation speed of the first travel motor 36L is set at ahigh speed (a second speed region up to a second maximum speed that isgreater than the first maximum speed; hereunder abbreviated as “secondspeed” as appropriate). That is, the rotation speed of the first travelmotor 36L can be changed to the first speed that is the low speed and tothe second speed that is the high speed.

The second travel motor 36R is a motor that transmits power to a driveshaft of the traveling device 5 provided on the right side of themachine body 2. The second travel motor 36R is rotatable by thehydraulic fluid delivered from the second travel pump 53R, and itsrotation speed can be changed by the flow rate of the hydraulic fluid. Aswash-plate switching cylinder 37R is connected to the second travelmotor 36R, and the rotation speed of the second travel motor 36R can bechanged even by extending and contracting the swash-plate switchingcylinder 37R in one direction or in the other direction. That is, whenthe swash-plate switching cylinder 37R is contracted, the rotation speedof the second travel motor 36R is set at a low speed (first speed), and,when the swash-plate switching cylinder 37R is extended, the rotationspeed of the second travel motor 36R is set at a high speed (secondspeed). That is, the rotation speed of the second travel motor 36R canbe changed to the first speed that is the low speed and to the secondspeed that is the high speed.

As shown in FIG. 1 , the hydraulic system of the working machine 1includes a travel switching valve 34. The travel switching valve 34 isswitchable to a first state in which the rotation speeds of the travelmotors 36 (the first travel motor 36L and the second travel motor 36R)can be increased up to the first maximum speed and to a second state inwhich the rotation speeds can be increased up to the second maximumspeed that is greater than the first maximum speed. The travel switchingvalve 34 includes first switching valves 71L and 71R and a secondswitching valve 72.

The first switching valve 71L is connected to the swash-plate switchingcylinder 37L at the first travel motor 36L via a fluid passage, and is atwo-position switching valve that switches to a first position 71L1 andto a second position 71L2. When the first switching valve 71L is in thefirst position 71L1, the swash-plate switching cylinder 37L iscontracted, and, when the first switching valve 71L is in the secondposition 71L2, the swash-plate switching cylinder 37L is extended.

The first switching valve 71R is connected to the swash-plate switchingcylinder 37R at the second travel motor 36R via a fluid passage, and isa two-position switching valve that switches to a first position 71R1and to a second position 71R2. When the first switching valve 71R is inthe first position 71R1, the swash-plate switching cylinder 37R iscontracted, and, when the first switching valve 71R is in the secondposition 71R2, the swash-plate switching cylinder 37R is extended.

The second switching valve 72 is a solenoid valve that switches thefirst switching valve 71L and the first switching valve 71R, and is atwo-position switching valve that is switchable to a first position 72 aand to a second position 72 b by energization. The second switchingvalve 72, the first switching valve 71L, and the first switching valve71R are connected to each other by a fluid passage 41. When the secondswitching valve 72 is in the first position 72 a, the first switchingvalve 71L and the first switching valve 71R are switched to the firstposition 71L1 and the first position 71R1, respectively, and, when thesecond switching valve 72 is in the second position 72 b, the firstswitching valve 71L and the first switching valve 71R are switched tothe second position 71L2 and the second position 71R2, respectively.

That is, when the second switching valve 72 is in the first position 72a, the first switching valve 71L is in the first position 71L1, and thefirst switching valve 71R is in the first position 71R1, the travelswitching valve 34 is brought into the first state and the rotationspeeds of the travel motors 36 (the first travel motor 36L and thesecond travel motor 36R) are set to the first speed. When the secondswitching valve 72 is in the second position 72 b, the first switchingvalve 71L is in the second position 71L2, and the first switching valve71R is in the second position 71R2, the travel switching valve 34 isbrought into the second state, and the rotation speeds of the travelmotors 36 (the first travel motor 36L and the second travel motor 36R)are set to the second speed.

Therefore, the travel motors 36 (the first travel motor 36L and thesecond travel motor 36R) can be switched to the first speed, which isthe low speed, and to the second speed, which is the high speed, by thetravel switching valve 34.

The travel motors 36 can be switched between the first speed and thesecond speed by a switching unit (switch 61). The switch 61 is, forexample, connected to a controller 60, and is operable to issue aspeed-change instruction of either increasing or decreasing speed inaccordance with the operation, for example, by an operator. The switch61 is switchable to either speed increase of switching from the firstspeed (the first state) to the second speed (the second state) and speeddecrease of switching from the second speed (the second state) to thefirst speed (the first state). That is, the switch 61 outputs aspeed-increase instruction (second-gear instruction) or a speed-decreaseinstruction (first-gear instruction) to the controller 60.

The controller 60 includes, for example, an electrical electroniccircuit and a semiconductor of a CPU, MPU, or the like. The controller60 switches the travel switching valve 34 on the basis of a switchingoperation of the switch 61. The switch 61 is a push switch. When theswitch 61 is pushed, for example, with the travel motors 36 in the firstspeed state, the switch 61 outputs the speed-increase instruction to thecontroller 60. The speed-increase instruction is an instruction thatcauses the travel motors 36 to be set to the second speed (instructionthat causes the travel switching valve 34 to be brought into the secondstate). When the switch 61 is pushed with the travel motors 36 in thesecond speed, the switch 61 outputs the speed-decrease instruction tothe controller 60. The speed-decrease instruction is an instruction thatcauses the travel motors 36 to be set to the first speed (instructionthat causes the travel switching valve 34 to be brought into the firststate). Note that the switch 61 may be a push switch that can bemaintained in an ON/OFF state. When the switch 61 is OFF, an instructionof maintaining the travel motors 36 in the first speed is output to thecontroller 60, and when the switch 61 is ON, an instruction ofmaintaining the travel motors 36 in the second speed is output to thecontroller 60.

When the controller 60 obtains the speed-decrease instruction, asolenoid of the second switching valve 72 is deenergized to bring thetravel switching valve 34 into the first state. When the controller 60obtains the speed-increase instruction, the solenoid of the secondswitching valve 72 is energized to bring the travel switching valve 34into the second state.

The hydraulic system of the working machine 1 includes a first hydraulicpump P1, a second hydraulic pump P2, and a travel operation device 54.The first hydraulic pump P1 is a pump that is driven by power of theprime mover 32 and includes a constant displacement gear pump. The firsthydraulic pump P1 is capable of delivering a hydraulic fluid stored in atank 22. In particular, the first hydraulic pump P1 delivers a hydraulicfluid primarily used for control. For explanatory convenience, the tank22 that stores a hydraulic fluid may be called a hydraulic-fluid tank.Of the hydraulic fluid delivered from the first hydraulic pump P1, ahydraulic fluid that is used for control is a pilot fluid, and thepressure of the pilot fluid is a pilot pressure.

The second hydraulic pump P2 is a pump that is driven by power of theprime mover 32 and includes a constant displacement gear pump. Thesecond hydraulic pump P2 is capable of delivering a hydraulic fluidstored in a tank 22, and supplies, for example, a hydraulic fluid to afluid passage of a working system. For example, the second hydraulicpump P2 supplies a hydraulic fluid to the boom cylinders 14 that operatethe booms 10, the bucket cylinders 15 that operate the bucket, and acontrol valve (flow-rate control valve) that operates and controls anauxiliary hydraulic pressure actuator.

The travel operation device 54 is a device that operates the travelpumps 53 (the first travel pump 53L and the second travel pump 53R), andthat is capable of changing the angle of the swash plate (swash-plateangle) of each travel pump 53. The travel operation device 54 includesan operation lever 59 (operation member) and a plurality of operationvalves 55.

The operation level 59 is an operation lever that is supported by theoperation valves 55 and that swings in a left-right direction(machine-body width direction) or the front-rear direction. That is,with reference to a neutral position N, the operation lever 59 can beoperated rightward and leftward from the neutral position N and can beoperated forward and rearward from the neutral position N. In otherwords, the operation lever 59 can be swung in at least four directionswith reference to the neutral position N. For explanatory convenience,the forward direction and the rearward direction, that is, thefront-rear direction is called a first direction. The rightwarddirection and the leftward direction, that is, the left-right direction(machine-body width direction) may be called a second direction.

The plurality of operation valves 55 are operated by a common, that is,one operation lever 59. The plurality of operation valves 55 areoperated on the basis of the swinging of the operation lever 59. Adelivery fluid passage 40 is connected to the plurality of operationvalves 55, and a hydraulic fluid (pilot fluid) from the first hydraulicpump P1 can be supplied to the plurality of operation valves 55 via thedelivery fluid passage 40. The plurality of operation valves 55 are anoperation valve 55A, an operation valve 55B, an operation valve 55C, andan operation valve 55D.

When the operation lever 59 has swung in the forward direction (onedirection) in the front-rear direction (first direction) (when theoperation lever 59 is operated forward), the operation valve 55A is suchthat the pressure of hydraulic fluid that is output in accordance withthe operation amount of a forward operation (operation) changes. Whenthe operation lever 59 has swung in the rearward direction (the otherdirection) in the front-rear direction (first direction) (when theoperation lever 59 is operated rearward), the operation valve 55B issuch that the pressure of hydraulic fluid that is output in accordancewith the operation amount of a rearward operation (operation) changes.When the operation lever 59 has swung in the rightward direction (onedirection) in the left-right direction (second direction) (when theoperation lever 59 is operated rightward), the operation valve 55C issuch that the pressure of hydraulic fluid that is output in accordancewith the operation amount of the rightward operation (operation)changes. When the operation lever 59 has swung in the leftward direction(the other direction) in the left-right direction (second direction)(when the operation lever 59 is operated leftward), the operation valve55D is such that the pressure of hydraulic fluid that is output inaccordance with the operation amount of the leftward operation(operation) changes.

The plurality of operation valves 55 and the travel pumps 53 (the firsttravel pump 53L and the second travel pump 53R) are connected to eachother by a travel fluid passage 45. In other words, the travel pumps 53(the first travel pump 53L and the second travel pump 53R) are pieces ofhydraulic equipment that can be operated by a hydraulic fluid that hasbeen output from the operation valves 55 (the operation valve 55A, theoperation valve 55B, the operation valve 55C, and the operation valve55D).

The travel fluid passage 45 has a first travel fluid passage 45 a, asecond travel fluid passage 45 b, a third travel fluid passage 45 c, afourth travel fluid passage 45 d, and a fifth travel fluid passage 45 e.The first travel fluid passage 45 a is a fluid passage that is connectedto the forward-movement pressure receiver 53 a of the first travel pump53L. The second travel fluid passage 45 b is a fluid passage that isconnected to the rearward-movement pressure receiver 53 b of the firsttravel pump 53L. The third travel fluid passage 45 c is a fluid passagethat is connected to the forward-movement pressure receiver 53 a of thesecond travel pump 53R. The fourth travel fluid passage 45 d is a fluidpassage that is connected to the rearward-movement pressure receiver 53b of the second travel pump 53R. The fifth travel fluid passage 45 e isa fluid passage that connects the operation valves 55, the first travelfluid passage 45 a, the second travel fluid passage 45 b, the thirdtravel fluid passage 45 c, and the fourth travel fluid passage 45 d.

When the operation lever 59 is swung forward (direction of arrow A1 inFIG. 1 ), the operation valve 55A is operated to output a pilot pressurefrom the operation valve 55A. The pilot pressure acts upon theforward-movement pressure receiver 53 a of the first travel pump 53L viathe first travel fluid passage 45 a and acts upon the forward-movementpressure receiver 53 a of the second travel pump 53R via the thirdtravel fluid passage 45 c. Therefore, the swash-plate angles of thefirst travel pump 53L and the second travel pump 53R are changed, andthe first travel motor 36L and the second travel motor 36R rotateforward (forward rotation) and thus the working machine 1 moves forwardin a straight line.

When the operation lever 59 is swung rearward (direction of arrow A2 inFIG. 1 ), the operation valve 55B is operated to output a pilot pressurefrom the operation valve 55B. The pilot pressure acts upon therearward-movement pressure receiver 53 b of the first travel pump 53Lvia the second travel fluid passage 45 b and acts upon therearward-movement pressure receiver 53 b of the second travel pump 53Rvia the fourth travel fluid passage 45 d. Therefore, the swash-plateangles of the first travel pump 53L and the second travel pump 53R arechanged, and the first travel motor 36L and the second travel motor 36Rrotate reversely (rearward rotation) and thus the working machine 1moves rearward in a straight line.

When the operation lever 59 is swung rightward (direction of arrow A3 inFIG. 1 ), the operation valve 55C is operated to output a pilot pressurefrom the operation valve 55C. The pilot pressure acts upon theforward-movement pressure receiver 53 a of the first travel pump 53L viathe first travel fluid passage 45 a and acts upon the rearward-movementpressure receiver 53 b of the second travel pump 53R via the fourthtravel fluid passage 45 d. Therefore, the swash-plate angles of thefirst travel pump 53L and the second travel pump 53R are changed, andthe first travel motor 36L rotates forward and the second travel motor36R rotates reversely and thus the working machine 1 swings toward theright.

When the operation lever 59 is swung leftward (direction of arrow A4 inFIG. 1 ), the operation valve 55D is operated to output a pilot pressurefrom the operation valve 55D. The pilot pressure acts upon theforward-movement pressure receiver 53 a of the second travel pump 53Rvia the third travel fluid passage 45 c and acts upon therearward-movement pressure receiver 53 b of the first travel pump 53Lvia the second travel fluid passage 45 b. Therefore, the swash-plateangles of the first travel pump 53L and the second travel pump 53R arechanged, and the first travel motor 36L rotates reversely and the secondtravel motor 36R rotates forward and thus the working machine 1 swingstoward the left.

When the operation lever 59 is swung in an oblique direction, a pressuredifference between the pilot pressure that acts upon theforward-movement pressure receiver 53 a and the pilot pressure that actsupon the rearward-movement pressure receiver 53 b causes the rotationdirections and the rotation speeds of the first travel motor 36L and thesecond travel motor 36R to be determined, and the working machine 1swings rightward or leftward while moving forward or rearward.

That is, when the operation lever 59 is swung obliquely leftward andforward, the working machine 1 swings leftward while moving forward at aspeed corresponding to the swing angle of the operation lever 59; whenthe operation lever 59 is swung obliquely rightward and forward, theworking machine 1 swings rightward while moving forward at a speedcorresponding to the swing angle of the operation lever 59; when theoperation lever 59 is swung obliquely leftward and rearward, the workingmachine 1 swings leftward while moving rearward at a speed correspondingto the swing angle of the operation lever 59; and, when the operationlever 59 is swung obliquely rightward and rearward, the working machine1 swings rightward while moving rearward at a speed corresponding to theswing angle of the operation lever 59.

An accelerator 65 operable to determine the rotation speed of the primemover is connected to the controller 60. The accelerator 65 is providednear the operator's seat 8. The accelerator 65 is, for example, anaccelerator lever that is swingably supported, an accelerator pedal thatis swingably supported, an accelerator volume that is rotatablysupported, or an accelerator slider that is slidably supported. Notethat the accelerator 65 is not limited to the examples above. A rotationdetector 66 to detect the rotation speed of the prime mover 32 isconnected to the controller 60. The controller 60 determines the actualrotation speed of the prime mover 32 by using the rotation detector 66.

The controller 60 sets a target prime-mover rotation speed (targetrotation speed) on the basis of the operation amount of the accelerator65 to control the actual rotation speed to become the set targetrotation speed.

A rotation detection sensor 64 that detects the rotation speeds and therotation directions of the travel motors 36 (the first travel motor 36Land the second travel motor 36R) is connected to the controller 60. Thecontroller 60 is capable of determining the rotation speeds and therotation directions of the travel motors 36.

When the travel switching valve 34 is switched from the first state tothe second state and when the travel switching valve 34 is switched fromthe second state to the first state, that is, when the rotation speedsof the travel motors 36 are to be increased from the first speed to thesecond speed and when the rotation speeds of the travel motors 36 are tobe decreased from the second speed to the first speed, the controller 60performs speed-change shock reduction control in which the supply amountof hydraulic fluid from the travel pumps 53 to the travel motors 36 isdecreased by decreasing the rotation speed of the prime mover 32 inaccordance with the travel speed of the machine body 2.

Note that, when there is a speed-change instruction with the workingmachine (machine body 2) in a traveling state, the controller 60decreases the rotation speed of the prime mover 32, whereas, even whenthere is a speed-change instruction with the working machine (machinebody 2) in a stopped state, the controller 60 does not decrease therotation speed of the prime mover 32.

FIG. 2A illustrates the relationship between the rotation speed (targetrotation speed, actual rotation speed) of the prime mover 32 when thespeed of a travel motor 36 is increased from the first speed to thesecond speed, and switching of the travel motor 36.

As shown in FIG. 2A, at a time point Q1, it is assumed that the switch61 has been operated and the controller 60 has obtained a speed-increaseinstruction (second-gear instruction) to change from the first state(the first speed) to the second state (the second speed). When thecontroller 60 obtains a second-gear instruction, the controller 60decreases an actual rotation speed W1 to a prescribed rotation speed W3that is lower than a target rotation speed W2 that has been set at theaccelerator 65. The prescribed rotation speed W3 is a rotation speedthat reduces speed-change shock occurring when the first speed isswitched to the second speed, and is, for example, a value obtained bysubtracting a decrease amount AD1 from the actual rotation speed W1.

The controller 60 sets the decrease amount AD1 in accordance with thetravel speed of the working machine (machine body) 2 that is one travelstate. Specifically, a travel detector 67 that detects the travel speedas a travel state is connected to the controller 60. The travel detector67 is a device that detects, for example, the pressure (pilot pressure)of hydraulic fluid (pilot fluid) that has been output from the operationvalves 55 (the operation valve 55A, the operation valve 55B, theoperation valve 55C, and the operation valve 55D), and that converts thedetected pilot pressure into travel speed. For example, when the pilotpressure of the travel fluid passage 45 is high, the travel speed isdetected as a high value; and, when the pilot pressure is low, thetravel speed is detected as a low value. Note that, although the traveldetector 67 detects the travel speed from the pilot pressure of thetravel fluid passage 45, instead, the travel detector 67 may be a devicethat detects the rotation speed of rotation shafts of the travel motors36 and that converts the detected rotation speed into a travel speed, ormay be any device that is capable of detecting the travel speed.

That is, when the controller 60 switches to speed increase, thecontroller 60 sets the decrease amount ΔD1 corresponding to the travelspeed detected by the travel detector 67, and decreases the rotationspeed of the prime mover in accordance with the set decrease amount 66D1.

As shown in FIG. 8A, the controller 60 stores decrease-amountcalculation data that indicates the relationship between the actualrotation speed W1, the pilot pressure of the travel fluid passage 45(travel pilot pressure), and the decrease amount ΔD1. FIG. 8B is a graphof FIG. 8A. Note that the decrease-amount calculation data in FIG. 8Aand FIG. 8B is only an example and is not limited thereto.

For example, as shown in FIG. 8A, when the controller 60 obtains asecond-gear instruction, if the actual rotation speed W1 is 3000 rpm andthe travel pilot pressure is 1.5 MPa, the decrease amount ΔD1 is set to500 rpm. Note that, as shown in FIG. 8A, when the controller 60decreases the rotation speed of the prime mover, the controller 60 setsa lower limit of the rotation speed of the prime mover so as not to belower than a minimum rotation speed of the prime mover. In decreasingthe rotation speed of the prime mover, even when the decrease amount ΔD1differs, the controller 60 sets at a constant value a gradient K1 inwhich the rotation speed of the prime mover is decreased (gradient at adecrease time T1).

As shown in FIG. 2A, when, at a time point Q2, the actual rotation speedW1 reaches the prescribed rotation speed W3, the controller 60 restoresthe actual rotation speed W1 to the target rotation speed W2.Alternatively, during the decrease time T1 in which the actual rotationspeed W1 is decreased to the prescribed rotation speed W3, thecontroller 60 restores the actual rotation speed W1 to the targetrotation speed W2. Here, the controller 60 causes a restoration time T2in which the actual rotation speed W1 is restored to the target rotationspeed W2 from the prescribed rotation speed W3 to be longer than thedecrease time T1. That is, the controller 60 causes a decrease speed atwhich the actual rotation speed W1 is decreased to the prescribedrotation speed W3 to be greater than a restoration speed at which theactual rotation speed W1 is restored from the prescribed rotation speedW3 to the target rotation speed W2.

At a timing in which a predetermined delay period has passed from thetime point Q1, that is, at a switching timing (timing during therestoration time T2 in FIG. 2A), the controller 60 outputs a signal toenergize a solenoid of the travel switching valve 34 and the travelswitching valve (switching valve) 34 is switched from the first state(the first speed) to the second state (the second speed). In otherwords, the controller 60 switches the travel switching valve 34 to thesecond state during the restoration time T2.

Note that the period of the restoration time T2 is a restoration periodfrom the time point Q2 when the actual rotation speed of the prime mover32 is decreased to a rotation speed (for example, the prescribedrotation speed W3) that is lower than the target rotation speed W2 towhen the actual rotation speed of the prime mover 32 is restored to thetarget rotation speed W2. In other words, the period of the restorationtime T2 can be said to be a restoration period in which the supplyamount to a travel motor 36 after being decreased is restored.

FIG. 3A is a flowchart of a first operation of the controller 60 whenthe rotation speed of a travel motor 36 is changed from the first speedto the second speed. Note that the working machine 1 is in a travellingstate instead of in a stopped state.

The controller 60 determines whether the switch 61 has been switchedfrom the first speed to the second speed (S1). When the switch 61 hasnot been switched to the second speed, that is, when the switch 61 ismaintained at the first speed (NO in S1), the controller 60 sets theactual rotation speed W1 to the target rotation speed W2 on the basis ofthe operation of the accelerator 65 (S2). When the switch 61 has beenswitched from the first speed to the second speed (YES in S1), thecontroller 60 determines whether a timing is the switching timing inwhich a predetermined delay period has passed from the time point Q1(S3). When the timing is not the switching timing (NO in S3), thecontroller 60 proceeds to S5. On the other hand, when the timing is theswitching timing (YES in S3), the controller 60 switches the travelswitching valve 34 from the first state (the first speed) to the secondstate (the second speed) (S4). In the case of NO in S3 or after S4, thecontroller 60 decreases the actual rotation speed W1 to the prescribedrotation speed W3 that is lower than the target rotation speed W2 (S5).

The controller 60 determines whether the actual rotation speed W1 hasreached the prescribed rotation speed W3 (S6), and when the actualrotation speed W1 has not reached the prescribed rotation speed W3 (NOin S6), the controller 60 returns to S3. On the other hand, when thecontroller 60 determines that the actual rotation speed W1 has reachedthe prescribed rotation speed W3 (YES in S6), the controller 60determines whether the timing is the switching timing (S7). When thetiming is the switching timing (YES in S7), the controller 60 switchesthe travel switching valve 34 from the first state (the first speed) tothe second state (second speed) (S8). On the other hand, when the timingis not the switching timing (NO in S7) or after S8, the controller 60restores the actual rotation speed W1 to the target rotation speed W2(S9). The controller 60 determines whether the actual rotation speed W1has been restored to the target rotation speed W2 (S10), and when thecontroller 60 determines that the actual rotation speed W1 has not beenrestored (NO in S10), the controller 60 returns to S7. Note that whenthe controller 60 determines that the actual rotation speed W1 has beenrestored to the target rotation speed W2 (YES in S10), the process ends.

FIG. 2B illustrates the relationship between the rotation speed (targetrotation speed, actual rotation speed) of the prime mover 32 when thespeed of a travel motor 36 is decreased from the second speed to thefirst speed, and switching of the travel motor 36.

As shown in FIG. 2B, at a time point Q11, it is assumed that the switch61 has been operated and the controller 60 has obtained a speed-decreaseinstruction (first-gear instruction) to change from the second state(the second speed) to the first state (the first speed). When thecontroller 60 obtains a first-gear instruction, the controller 60decreases the actual rotation speed W1 to a prescribed rotation speed W4that is lower than the target rotation speed W2 that has been set by theaccelerator 65. The prescribed rotation speed W4 is a rotation speed atwhich a speed-change shock occurring when the second speed is switchedto the first speed is reduced, and is set, for example, by the decreaseamount ΔD1 from the target rotation speed W2. Note that the setting ofthe decrease amount ΔD1 is the same as that in the embodiment above, andwhen the controller 60 switches to speed decrease, the controller 60sets the decrease amount AD1 corresponding to the travel speed detectedby the travel detector 67, and decreases the rotation speed of the primemover in accordance with the set decrease amount ΔD1. In decreasing therotation speed of the prime mover, even when the decrease amount ΔD1differs, the controller 60 sets at a constant value a gradient K2 inwhich the rotation speed of the prime mover is decreased (gradient at adecrease time T11).

As shown in FIG. 2B, when, at a time point Q12, the actual rotationspeed W1 reaches the prescribed rotation speed W4, the controller 60restores the actual rotation speed W1 to the target rotation speed W2.Alternatively, during a decrease time T11 in which the actual rotationspeed W1 is decreased to the prescribed rotation speed W4, thecontroller 60 restores the actual rotation speed W1 to the targetrotation speed W2. Here, the controller 60 causes a restoration time T12in which the actual rotation speed W1 is restored to the target rotationspeed W2 from the prescribed rotation speed W4 to be shorter than thedecrease time T11. That is, the controller 60 causes a decrease speed atwhich the actual rotation speed W1 is decreased to the prescribedrotation speed W4 to be less than a restoration speed at which theactual rotation speed W1 is restored to the target rotation speed W2from the prescribed rotation speed W4.

At a switching timing in which a predetermined delay period has passedfrom the time point Q11 (for example, timing during the decrease timeT11), the controller 60 outputs a signal to deenergize the solenoid ofthe travel switching valve 34 (switching valve) to switch the travelswitching valve 34 from the second state (the second speed) to the firststate (the first speed). In other words, the controller 60 restores theactual rotation speed W1 to the target rotation speed W2 after switchingthe travel switching valve 34 to the first state during the decreasetime T11.

Note that a period of the decrease time T11 is a decrease period fromwhen the actual rotation speed of the prime mover 32 starts decreasing(for example, the time point Q11) to when the actual rotation speed ofthe prime mover 32 is decreased to a rotation speed (for example, theprescribed rotation speed W4) that is lower than the target rotationspeed W2. In other words, the period of the decrease time T11 can besaid to be a decrease period in which the supply amount to a travelmotor 36 is decreased.

FIG. 3B is a flowchart of a second operation of the controller 60 whenthe rotation speed of a travel motor is changed from the second speed tothe first speed. Note that the working machine is in a travelling stateinstead of in a stopped state.

The controller 60 determines whether the switch 61 has been switchedfrom the second speed to the first speed (S11). When the switch 61 hasnot switched to the first speed, that is, when the switch 61 ismaintained at the second speed (NO in S11), the controller 60 sets theactual rotation speed W1 to the target rotation speed W2 on the basis ofthe operation of the accelerator 65 (S12). When the switch 61 has beenswitched from the second speed to the first speed (YES in S11), thecontroller 60 determines whether a timing is a switching timing (S13).When the timing is not the switching timing (NO in S13), the controller60 proceeds to S15. On the other hand, when the timing is the switchingtiming (YES in S13), the controller 60 switches the travel switchingvalve 34 from the second state (the second speed) to the first state(the first speed) (S14). In the case of NO in S13 or after S14, thecontroller 60 decreases the actual rotation speed W1 to the prescribedrotation speed W4 that is lower than the target rotation speed W2 (S15).The controller 60 determines whether the actual rotation speed W1 hasreached the prescribed rotation speed W4 (S16), and when the actualrotation speed W1 has not reached the prescribed rotation speed W4 (NOin S16), the controller 60 returns to S13. On the other hand, when thecontroller 60 determines that the actual rotation speed W1 has reachedthe prescribed rotation speed W4 (YES in S16), the controller 60determines whether the timing is the switching timing (S17). When thetiming is the switching timing (YES in S17), the controller 60 switchesthe travel switching valve 34 from the second state (the second speed)to the first state (first speed) (S18). On the other hand, when thetiming is not the switching timing (NO in S17) or after S18, thecontroller 60 restores the actual rotation speed W1 to the targetrotation speed W2 (S19). The controller 60 determines whether the actualrotation speed W1 has been restored to the target rotation speed W2(S20), and when the controller 60 determines that the actual rotationspeed W1 has not been restored (NO in S20), the controller 60 returns toS17. Note that when the controller 60 determines that the actualrotation speed W1 has been restored to the target rotation speed W2 (YESin S20), the process ends.

A plurality of pressure detectors 80 (travel pressure detectors) areconnected to a circulation fluid passage 57 h. The plurality of pressuredetectors 80 include a first pressure detector 80 a and a secondpressure detector 80 b. A plurality of pressure detectors 80 areconnected to a circulation fluid passage 57 i. The plurality of pressuredetectors 80 include a third pressure detector 80 c and a fourthpressure detector 80 d. The first pressure detector 80 a to the fourthpressure detector 80 d are each connected to the controller 60.

Specifically, the first pressure detector 80 a is, in the circulationfluid passage 57 h, provided on a side of a first port P11 of the firsttravel motor 36L, and the pressure at the first port P11 is detected asa first travel pressure V1. The second pressure detector 80 b is, in thecirculation fluid passage 57 h, provided on a side of a second port P12of the first travel motor 36L, and the pressure at the second port P12is detected as a second travel pressure V2. The third pressure detector80 c is, in the circulation fluid passage 57 i, provided on a side of athird port P13 of the second travel motor 36R, and the pressure at thethird port P13 is detected as a third travel pressure V3. The fourthpressure detector 80 d is, in the circulation fluid passage 57 i,provided on a side of a fourth port P14 of the second travel motor 36R,and the pressure at the fourth port P14 is detected as a fourth travelpressure V4.

The first port P11 is a suction port when the first travel motor 36Lrotates forward, and the second port P12 is a delivery port when thefirst travel motor 36L rotates forward. The third port P13 is a suctionport when the second travel motor 36R rotates forward, and the fourthport P14 is a delivery port when the second travel motor 36R rotatesforward.

When a change in speed has occurred while the machine body 2 (theworking machine 1) is moving forward (that is, the first travel motor36L and the second travel motor 36R are rotating forward), the firsttravel pressure V1 that is detected at the first pressure detector 80 aand the third travel pressure V3 that is detected at the third pressuredetector 80 c are called forward-movement travel pressures, and thesecond travel pressure V2 that is detected at the second pressuredetector 80 b and the fourth travel pressure V4 that is detected at thefourth pressure detector 80 d are called rearward-movement travelpressures.

When a change in speed has occurred while the machine body 2 (theworking machine 1) is moving rearward (that is, the first travel motor36L and the second travel motor 36R are rotating reversely), conversely,the first travel pressure V1 that is detected at the first pressuredetector 80 a and the third travel pressure V3 that is detected at thethird pressure detector 80 c are called rearward-movement travelpressures, and, conversely, the second travel pressure V2 that isdetected at the second pressure detector 80 b and the fourth travelpressure V4 that is detected at the fourth pressure detector 80 d arecalled forward-movement travel pressures.

In accordance with the travel pressures detected by the pressuredetectors 80 (travel pressure detectors) at the time of a speed-changeinstruction, the controller 60 changes a delay period lasting up to theswitching timing of the travel switching valve 34 from an output timingof the speed-change instruction of the switching unit (switch 61).

The pressure detectors 80 each detect, as a forward-movement travelpressure, the pressure of hydraulic fluid that is supplied to the travelmotors 36 that are rotating forward from the travel pumps 53.Specifically, the first pressure detector 80 a detects the first travelpressure V1 as a forward-movement travel pressure, and the thirdpressure detector 80 c detects the third travel pressure V3 as aforward-movement travel pressure. At least one of the first pressuredetector 80 a and the third pressure detector 80 c corresponds to afirst travel pressure detector. At the time of a speed-changeinstruction of increasing speed or decreasing speed, in accordance withthe forward-movement travel pressures (that is, the first travelpressure V1 and the third travel pressure V3) detected by the firstpressure detector 80 a and the third pressure detector 80 c, thecontroller 60 changes the delay period. In the first embodiment,although, in the controller 60, the higher of the first travel pressureV1 and the third travel pressure V3 is the forward-movement travelpressure, the smaller of the first travel pressure V1 and the thirdtravel pressure V3 may be the forward-movement travel pressure.Alternatively, in the controller 60, both the first travel pressure V1and the third travel pressure V3 may be the forward-movement travelpressures, or the average value of the first travel pressure V1 and thethird travel pressure V3 may be the forward-movement travel pressure.

Specifically, when there has been a second-gear instruction while themachine body 2 is moving forward (forward-movement speed-increase), ifthe forward-movement travel pressure exceeds a threshold value (forexample, a speed-increase first threshold value), the controller 60decreases the delay period. When there has been a first-gear instructionwhile the machine body 2 is moving forward (forward-movementspeed-decrease), if the forward-movement travel pressure exceeds athreshold value (for example, a speed-decrease second threshold value),the controller 60 decreases the delay period.

The controller 60 includes a memory 60 a having a memory table TB (seeFIG. 2C). The memory table TB stores threshold values (for example, thespeed-increase first threshold value and the speed-decrease secondthreshold value), central values each indicating a predetermined periodfrom the output timing of the speed-change instruction of the switch 61,first values each indicating a first period that is shorter than theperiod indicated by the central value, and second values each indicatinga second period that is longer than the period indicated by the centralvalue. FIG. 2C illustrates data when the rotation speed of the primemover 32 is a certain rotation speed RTn (for example, n=1500 to 3000rpm). When the operation lever 59 is operated forward and the machinebody 2 is moving forward and when a speed-increase operation or aspeed-decrease operation is performed (that is, there has been thespeed-increase instruction (second-gear instruction) or thespeed-decrease instruction (first-gear instruction) by the switch 61,the controller 60 determines whether at least one of theforward-movement travel pressures detected by the first pressuredetector 80 a and the third pressure detector 80 c (here, the higher ofthe first travel pressure V1 and the third travel pressure V3) exceedsthe threshold value (for example, the speed-increase first thresholdvalue at the time of speed increase, or the speed-decrease secondthreshold value at the time of speed decrease). When the controller 60determines that the threshold value is not exceeded, the controller 60causes the central value to be the delay period, and when the controller60 determines that the threshold value is exceeded, the controller 60causes the first value to be the delay period.

In the case of the forward-movement speed decrease, in addition to theforward-movement travel pressure above being detected, the pressuredetectors 80 each detect, as a rearward-movement travel pressure, thepressure of hydraulic fluid that is delivered from the travel motors 36that are rotating forward to the travel pumps 53. Specifically, thesecond pressure detector 80 b detects the second travel pressure V2 as arearward-movement travel pressure, and the fourth pressure detector 80 ddetects the fourth travel pressure V4 as a rearward-movement travelpressure. At least one of the second pressure detector 80 b and thefourth pressure detector 80 d corresponds to a second travel pressuredetector. At the time of a speed-change instruction of decreasing speed,in accordance with the rearward-movement travel pressures (that is, thesecond travel pressure V2 and the fourth travel pressure V4) detected bythe second pressure detector 80 b and the fourth pressure detector 80 d,the controller 60 changes the delay period. In the first embodiment,although, in the controller 60, the higher of the second travel pressureV2 and the fourth travel pressure V4 is the rearward-movement travelpressure, the smaller of the second travel pressure V2 and the fourthtravel pressure V4 may be the rearward-movement travel pressure.Alternatively, in the controller 60, both the second travel pressure V2and the fourth travel pressure V4 may be the rearward-movement travelpressures, or the average value of the second travel pressure V2 and thefourth travel pressure V4 may be the rearward-movement travel pressure.

Specifically, when there has been a first-gear instruction while themachine body 2 is moving forward (forward-movement speed-decrease), ifthe forward-movement travel pressure does not exceed the speed-decreasesecond threshold value, and, if the rearward—movement travel pressureexceeds the speed-decrease second threshold value, the controller 60increases the delay period. For example, when the operation lever 59 isoperated forward and the machine body 2 is moving forward, and when aspeed-decrease operation is performed (that is, when there has been thespeed-decrease instruction (first-gear instruction) by the switch 61,the controller 60 determines whether at least one of therearward-movement travel pressures detected by the second pressuredetector 80 b and the fourth pressure detector 80 d (here, the higher ofthe second travel pressure V2 and the fourth travel pressure V4) exceedsthe speed-decrease second threshold value. When the controller 60determines that the speed-decrease second threshold value is notexceeded, the controller 60 causes the central value to be the delayperiod, and when the controller 60 determines that the speed-decreasesecond threshold value is exceeded, the controller 60 causes the secondvalue to be the delay period.

The memory 60 a stores the threshold values (the speed-increase firstthreshold value and the speed-decrease second threshold value), thecentral values, and the first and second values) according to therotation speed of the prime mover 32. The controller 60 uses any one ofthe threshold values, the central values, and the first and secondvalues corresponding to the rotation speed of the prime mover 32detected by the rotation detector 66. Note that, although the thresholdvalue when the speed-increase operation is performed (speed-increasefirst threshold value) and the threshold value when the speed-decreaseoperation is performed (speed-decrease second threshold value) differfrom each other, they may be the same.

On the basis of an operation of an operator, the controller 60 isswitchable from an ordinary mode to a setting mode of setting aspeed-change switching timing, and, when a mode is the setting mode, thecontroller 60 causes the machine body 2 (working machine 1) to actuallytravel (to be in an actual travel state) or to idle (to not be in theactual travel state) to change the delay period when the threshold valueis exceeded. Note that, in the ordinary mode, when the threshold valueis exceeded, the controller 60 may change the delay period. When thedelay period is changed in the ordinary mode, the delay period afterbeing changed is used when the next speed-change instruction is used.

Here, an operation of changing the speed-change switching delay periodof the controller 60 at the time of forward-movement speed-increase isdescribed by using FIG. 3C.

When the operation lever 59 is operated forward and the machine body 2is moving forward (that is, when the rotation directions of the firsttravel motor 36L and the second travel motor 36R are forward directionsas detected by the rotation detection sensor 64), the controller 60determines whether there is a speed-increase instruction (second-gearinstruction) by the switch 61 (S51). When the controller 60 has notreceived a second-gear instruction (NO in S51), the controller 60returns to S51 and the controller 60 stands by until the controller 60receives a second-gear instruction. On the other hand, when thecontroller 60 has received a second-gear instruction from the switch 61,the controller 60 determines that the speed is to be increased duringthe forward movement (YES in S51), and obtains the rotation speed of theprime mover 32 by using the rotation detector 66 (S52). The controller60 obtains from the memory table TB a threshold value corresponding tothe rotation speed of the prime mover 32 (speed-increase first thresholdvalue) (S53).

The controller 60 obtains at least one of the forward-movement travelpressures detected by the first pressure detector 80 a and the thirdpressure detector 80 c (here, the higher of the first travel pressure V1and the third travel pressure V3) (S54). The controller 60 determineswhether the forward-movement travel pressure (here, the higher of thefirst travel pressure V1 and the third travel pressure V3) exceeds thethreshold value (for example, the speed-increase first threshold value)(S55). When the forward-movement travel pressure exceeds thespeed-increase first threshold value (YES in S55), the controller 60selects, as a delay period, the first value that is smaller than thecentral value (S56). That is, as shown in FIG. 2C and FIG. 2D, thecontroller 60 changes the delay period from the central value (60milliseconds) to the first value (40 milliseconds). As shown in FIG. 2A,a delay period Z10 that has been the central value (60 milliseconds) ischanged to a delay period Z10A that is shorter than the delay periodZ10.

On the other hand, when the forward-movement travel pressure does notexceed the speed-increase first threshold value (NO in S55), as shown inFIG. 2C and FIG. 2D, the controller 60 maintains the delay period at thecentral value (60 milliseconds) (S57). As shown in FIG. 2A, the delayperiod Z10 is maintained at the central value (60 milliseconds).

Next, an operation of changing the speed-change switching delay periodof the controller 60 at the time of forward-movement speed-decrease isdescribed by using FIG. 3D.

When the operation lever 59 is operated forward and the machine body 2is moving forward (that is, when the rotation directions of the firsttravel motor 36L and the second travel motor 36R detected by therotation detection sensor 64 are forward directions), the controller 60determines whether there has been a speed-decrease instruction(first-gear instruction) by the switch 61 (S61). When the controller 60has not received a first-gear instruction (NO in S61), the controller 60returns to S61 and the controller 60 stands by until the controller 60receives a first-gear instruction. On the other hand, when thecontroller 60 has received a first-gear instruction from the switch 61,the controller 60 determines that the speed is to be decreased duringthe forward movement (YES in S61), and obtains the rotation speed of theprime mover 32 by using the rotation detector 66 (S62). The controller60 obtains from the memory table TB a threshold value corresponding tothe rotation speed of the prime mover 32 (speed-decrease secondthreshold value) (S63).

The controller 60 obtains at least one of the forward-movement travelpressures detected by the first pressure detector 80 a and the thirdpressure detector 80 c (here, the higher of the first travel pressure V1and the third travel pressure V3) (S64). The controller 60 determineswhether the forward-movement travel pressure (here, the higher of thefirst travel pressure V1 and the third travel pressure V3) exceeds thethreshold value (for example, the speed-decrease second threshold value)(S65). When the forward-movement travel pressure exceeds thespeed-decrease second threshold value (YES in S65), the controller 60selects, as a delay period, the first value that is smaller than thecentral value (S66). That is, as shown in FIG. 2C and FIG. 2D, thecontroller 60 changes the delay period from the central value (680milliseconds) to the first value (660 milliseconds). As shown in FIG.2B, a delay period Z11 that has been the central value (680milliseconds) is changed to a delay period Z11B that is shorter than thedelay period Z11.

On the other hand, when the forward-movement travel pressure does notexceed the speed-decrease second threshold value (NO in S65), thecontroller 60 obtains at least one of the rear-movement travel pressuresdetected by the second pressure detector 80 b and the fourth pressuredetector 80 d (here, the higher of the second travel pressure V2 and thefourth travel pressure V4) (S67). The controller 60 determines whetherthe rear-movement travel pressure (here, the higher of the second travelpressure V2 and the fourth travel pressure V4) exceeds a threshold value(for example, the speed-decrease second threshold value) (S68). When therear-movement travel pressure does not exceed the speed-decrease secondthreshold value (NO in S68), the controller 60 maintains the delayperiod at the central value (680 milliseconds) (S69). As shown in FIG.2B, the delay period Z11 is maintained at the central value (680milliseconds).

On the other hand, when the rearward-movement travel pressure exceedsthe speed-decrease second threshold value (YES in S68), the controller60 selects, as a delay period, the second value that is larger than thecentral value (S70). That is, as shown in FIG. 2C and FIG. 2D, thecontroller 60 changes the delay period from the central value (680milliseconds) to the second value (700 milliseconds). As shown in FIG.2B, a delay period Z11 that has been the central value (680milliseconds) is changed to a delay period Z11A that is longer than thedelay period Z11.

The working machine 1 of the first embodiment above includes a primemover 32, travel pumps 53 that are operated by power of the prime mover32 and that deliver a hydraulic fluid, travel motors 36 that arerotatable by the hydraulic fluid delivered by the travel pumps 53, amachine body 2 where the prime mover 32, the travel pumps 53, and thetravel motors 36 are provided, a travel switching valve 34 that isswitchable to the first state in which the rotation speed of the travelmotors 36 can be increased up to the first maximum speed and to thesecond state in which the rotation speed of the travel motors 36 can beincreased up to the second maximum speed that is greater than the firstmaximum speed, a travel operation device 54 that has operation valvesthat are capable of changing the pressure of the hydraulic fluid thatacts upon the travel pumps 53 in accordance with the operation of anoperation lever 59 (operation member), a controller 60 that decreases asupply amount of the hydraulic fluid from the travel pumps 53 to thetravel motors 36 on the basis of the travel state of the machine body 2when performing either one of the speed-increase operation of switchingfrom the first state to the second state and the speed-decreaseoperation of switching from the second state to the first state, aswitch 61 (switching unit) operable to issue a speed-change instructionof either increasing or decreasing speed, and pressure detectors 80(travel pressure detectors) that detect, as a travel pressure, thepressure of the hydraulic fluid that the travel pumps 53 deliver to thetravel motors 36 at the time of the speed-change instruction. Inaccordance with the travel pressure detected by the pressure detectors80 at the time of the speed-change instruction, the controller 60changes a delay period lasting up to a switching timing of the travelswitching valve 34 from an output timing of the speed-change instructionof the switch 61.

According to this structure, in accordance with the travel pressure atthe time of the speed-change instruction, the controller 60 changes thedelay period lasting up to the switching timing of the travel switchingvalve 34 from the output timing of the speed-change instruction of theswitch 61. Therefore, with regard to the working machine 1 in whichthere is a shift in the speed-change timing resulting from variations ina delay in responding to the rotation of hydraulic equipment or theprime mover 32, an adjustment of reducing a speed-change shock can beperformed.

The pressure detectors 80 include first travel pressure detectors (firstpressure detector 80 a and third pressure detector 80 c) that detect, asforward-movement travel pressures, the pressure of hydraulic fluid thatis supplied to the travel motors 36 that are rotating forward from thetravel pumps 53. In accordance with the forward-movement travelpressures (first travel pressure V1 and third travel pressure V3)detected by the first pressure detector 80 a and the third pressuredetector 80 c at the time of a speed-change instruction of increasingspeed or decreasing speed, the controller 60 changes the delay period.In this structure, in accordance with the forward-movement travelpressures when the working machine 1 moves forward and a speed-increaseoperation or a speed-decrease operation is performed, the controller 60changes the delay period lasting up to the switching timing of thetravel switching valve 34 from the output timing of the speed-changeinstruction of increasing speed or decreasing speed at the time of theforward movement. Therefore, with regard to the working machine 1 inwhich there is a shift in the speed-change timing resulting fromvariations in a delay in responding to the rotation of hydraulicequipment or the prime mover 32, an adjustment of reducing aspeed-change shock occurring when the speed is increased or decreased atthe time of the forward movement of the working machine 1 can beperformed.

When the forward-movement travel pressures (the first travel pressure V1and the third travel pressure V3) detected by the first travel pressuredetectors (the first pressure detector 80 a and the third pressuredetector 80 c) at the time of a speed-change instruction of increasingspeed exceed a threshold value, the controller 60 decreases the delayperiod. According to this structure, when the forward-movement travelpressures when the working machine 1 moves forward and a speed-increaseoperation is performed exceed the threshold value, the controller 60decreases the delay period lasting up to the switching timing of thetravel switching valve 34 from the output timing of the speed-changeinstruction of increasing speed at the time of the forward movement.Therefore, with regard to the working machine 1 in which there is ashift in the speed-change timing resulting from variations in a delay inresponding to the rotation of hydraulic equipment or the prime mover 32,a speed-change shock occurring when the speed is increased at the timeof the forward movement of the working machine 1 can be reduced.

When the forward-movement travel pressures (the first travel pressure V1and the third travel pressure V3) detected by the first travel pressuredetectors (the first pressure detector 80 a and the third pressuredetector 80 c) at the time of a speed-change instruction of decreasingspeed exceed a threshold value, the controller 60 decreases the delayperiod. According to this structure, when the forward-movement travelpressures when the working machine 1 moves forward and a speed-decreaseoperation is performed exceed the threshold value, the controller 60decreases the delay period lasting up to the switching timing of thetravel switching valve 34 from the output timing of the speed-changeinstruction of decreasing speed at the time of the forward movement.Therefore, with regard to the working machine 1 in which there is ashift in the speed-change timing resulting from variations in a delay inresponding to the rotation of hydraulic equipment or the prime mover 32,a speed-change shock occurring when the speed is decreased at the timeof the forward movement of the working machine 1 can be reduced.

The pressure detectors 80 include second travel pressure detectors(second pressure detector 80 b and fourth pressure detector 80 d) thatdetect, as rearward-movement travel pressures, the pressure of hydraulicfluid that is delivered from the travel motors 36 that are rotatingforward to the travel pumps 53. When the rearward-movement travelpressures (second travel pressure V2 and fourth travel pressure V4)detected by the second pressure detector 80 b and the fourth pressuredetector 80 d at the time of a speed-change instruction of decreasingspeed exceeds a threshold value, the controller 60 increases the delayperiod. According to this structure, when the rearward movement travelpressures when the working machine 1 moves forward and the speed isdecreased exceed the threshold value, the controller 60 increases thedelay period lasting up to the switching timing of the travel switchingvalve 34 from the output timing of a speed-change instruction ofdecreasing speed at the time of the forward movement. Therefore, withregard to the working machine 1 in which there is a shift in thespeed-change timing resulting from variations in a delay in respondingto the rotation of hydraulic equipment or the prime mover 32, aspeed-change shock occurring when the speed is decreased at the time ofthe forward movement of the working machine 1 can be suitably reduced.

When the controller 60 is in the setting mode of setting a speed-changeswitching timing, the controller 60 changes the delay period. Accordingto this structure, when the controller 60 is in the setting mode ofsetting a speed-change switching timing, an adjustment of reducing aspeed-change shock can be performed.

The controller 60 includes a memory 60 a having a memory table TB thatstores at least threshold values, central values each indicating apredetermined period from the output timing of the speed-changeinstruction of the switch 61, and first values each indicating a firstperiod that is shorter than the period indicated by the central value.When the operation lever 59 is operated forward and when aspeed-increase operation or a speed-decrease operation is performed, thecontroller 60 determines whether the forward-movement travel pressures(the first travel pressure V1 and the third travel pressure V3) detectedby the first travel pressure detectors (the first pressure detector 80 aand the third pressure detector 80 c) exceed the threshold value. Whenthe controller 60 determines that the threshold value is not exceeded,the controller 60 causes the central value to be the delay period, andwhen the controller 60 determines that the threshold value is exceeded,the controller 60 causes the first value to be the delay period.According to this structure, when the controller 60 determines that theforward-movement travel pressures when the working machine 1 movesforward and a speed-increase operation or a speed-decrease operation isperformed exceed the threshold value, the controller 60 changes thedelay period lasting up to the switching timing of the travel switchingvalve 34 from the output timing of the speed-change instruction ofincreasing or decreasing speed at the time of the forward movement tothe first value that is a period shorter than the period indicated bythe central value. Therefore, with regard to the working machine 1 inwhich there is a shift in the speed-change timing resulting fromvariations in a delay in responding to the rotation of hydraulicequipment or the prime mover 32, a speed-change shock occurring when thespeed is increased or decreased at the time of the forward movement ofthe working machine 1 can be suitably reduced by changing the delayperiod to the first value that is smaller than the central value.

The controller 60 includes the memory 60 a having the memory table TBthat stores at least threshold values, central values each indicating apredetermined period from the output timing of the speed-changeinstruction of the switch 61, and second values each indicating a secondperiod that is longer than the period indicated by the central value.When the operation lever 59 is operated forward and when the speed isdecreased, the controller 60 determines whether the rearward-movementtravel pressures (the second travel pressure V2 and the fourth travelpressure V4) detected by the second travel pressure detectors (thesecond pressure detector 80 b and the fourth pressure detector 80 d)exceed the threshold value. When the controller 60 determines that thethreshold value is not exceeded, the controller 60 causes the centralvalue to be the delay period, and when the controller 60 determines thatthe threshold value is exceeded, the controller 60 changes the centralvalue and causes the second value to be the delay period. According tothis structure, when the controller 60 determines that therearward-movement travel pressures when the working machine 1 movesforward and the speed is decreased exceed the threshold value, thecontroller 60 changes, as the delay period, the period lasting up to theswitching timing of the travel switching valve 34 from the output timingof the speed-change instruction of decreasing speed at the time of theforward movement to the second value that is a period longer than theperiod indicated by the central value. Therefore, with regard to theworking machine 1 in which there is a shift in the speed-change timingresulting from variations in a delay in responding to the rotation ofhydraulic equipment or the prime mover 32, a speed-change shockoccurring when the speed is decreased at the time of the forwardmovement can be suitably reduced by changing the delay period to thesecond value that is larger than the central value when the speed-changeshock is insufficiently reduced when the central value is used.

A rotation detector 66 that detects the rotation speed of the primemover 32 is provided. The memory 60 a stores the threshold values, thecentral values, and the first values according to the rotation speed ofthe prime mover 32, and the controller 60 uses any one of the thresholdvalues, the central values, and the first values corresponding to therotation speed of the prime mover 32 detected by the rotation detector66. According to this structure, since the memory 60 a stores thethreshold values, the central values, and the first values according tothe rotation speed of the prime mover 32, a speed-change shock can besuitably reduced in correspondence with the rotation speed of the primemover 32.

The rotation detector 66 that detects the rotation speed of the primemover 32 is provided. The memory 60 a stores the threshold values, thecentral values, and the second values according to the rotation speed ofthe prime mover 32, and the controller 60 uses any one of the thresholdvalues, the central values, and the second values corresponding to therotation speed of the prime mover 32 detected by the rotation detector66. According to this structure, since the memory 60 a stores thethreshold values, the central values, and the second values according tothe rotation speed of the prime mover 32, a speed-change shock can besuitably reduced in correspondence with the rotation speed of the primemover 32.

The threshold value when a speed-increase operation is performed (thespeed-increase first threshold value) and the threshold value when aspeed-decrease operation is performed (the speed-decrease secondthreshold value) differ from each other. According to this structure,since a threshold value that differs when the speed-increase operationis performed from when the speed-decrease operation is performed isused, the delay period can be suitably set when the speed-increaseoperation is performed and when the speed-decrease operation isperformed.

In the working machine 1 of the first embodiment above, when aspeed-increase operation is performed, the controller 60 switches thetravel switching valve 34 from the first state to the second state in arestoration period in which the rotation speed of the prime mover 32after being decreased from the target rotation speed W2 that is therotation speed of the prime mover 32 determined by operating theaccelerator 65 is restored (for example, the period of the restorationtime T2 shown in FIG. 2A). That is, the controller 60 switches thetravel switching valve 34 from the first state to the second state inthe restoration period in which the supply amount to the travel motors36 after being decreased is restored. Therefore, with regard to theworking machine 1 in which there is a shift in the speed-change timingresulting from variations in a delay in responding to the rotation ofhydraulic equipment or the prime mover 32, a speed-change shock can besuitably reduced when the speed-increase operation is performed.Therefore, with regard to the working machine 1 in which a shift in thespeed-change timing occurs when the speed is increased, a speed-changeshock can be suitably reduced.

The controller 60 switches the travel switching valve 34 from the secondstate to the first state in a decrease period in which the rotationspeed of the prime mover 32 is decreased from the target rotation speedW2 determined by operating the accelerator 65 (for example, the periodof the decrease time T11 shown in FIG. 2B). That is, when aspeed-decrease operation is performed, the controller 60 switches thetravel switching valve 34 from the second state to the first state inthe decrease period up to when the supply amount to the travel motors 36starts decreasing. Therefore, with regard to the working machine 1 inwhich there is a shift in the speed-change timing resulting fromvariations in a delay in responding to the rotation of hydraulicequipment or the prime mover 32, a speed-change shock occurring when thespeed-decrease operation is performed can be suitably reduced.Therefore, with regard to the working machine 1 in which a shift in thespeed-change timing occurs when the speed is decreased, a speed-changeshock can be suitably reduced.

As described above, the controller 60 is capable of changing the delayperiod lasting up to the switching timing of the travel switching valve34 from the output timing of the speed-change instruction of the switch61 in accordance with the travel pressures detected by the pressuredetectors 80 (travel pressure detectors) at the time of a speed-changeinstruction. Therefore, the controller 60 is capable of changing thedelay period to a prior period shown in FIG. 2G and FIG. 2H or anafter-restoration period shown in FIG. 2E and FIG. 2F.

Here, the case in which delay periods Z10B and Z11C are set at priorperiods shown in FIG. 2G and FIG. 2H is described. When a speed-increaseoperation is performed, the controller 60 may switch the travelswitching valve 34 from the first state to the second state in a priorperiod lasting up to when the supply amount to the travel motors 36starts decreasing (for example, as shown in FIG. 2G, a prior period T1Alasting up to when the rotation speed of the prime mover 32 startsdecreasing). When the controller 60 sets the delay period Z10B withinthe prior period T1A, the controller 60 switches the travel switchingvalve 34 from the second state to the first state in S4 shown in FIG.3A. In this case, with regard to the working machine 1 in which there isa shift in the speed-change timing resulting from variations in a delayin responding to the rotation of hydraulic equipment or the prime mover32, a speed-change shock occurring when the speed-increase operation isperformed can be suitably reduced. When a speed-decrease operation isperformed, the controller 60 may switch the travel switching valve 34from the second state to the first state in a prior period lasting up towhen the supply amount to the travel motors 36 starts decreasing (forexample, as shown in FIG. 2H, a prior period T1A lasting up to when therotation speed of the prime mover 32 starts decreasing). When thecontroller 60 sets the delay period Z11C within the prior period T1A,the controller 60 switches the travel switching valve 34 from the secondstate to the first state in S14 shown in FIG. 3B. In this case, withregard to the working machine 1 in which there is a shift in thespeed-change timing resulting from variations in a delay in respondingto the rotation of hydraulic equipment or the prime mover 32, aspeed-change shock occurring when the speed-decrease operation isperformed can be suitably reduced.

Next, the case in which the delay periods Z14 and Z15 are set atrestoration periods shown in FIG. 2E and FIG. 2F is described. When aspeed-increase operation is performed, the controller 60 may switch thetravel switching valve 34 from the first state to the second state in anafter-restoration period (for example, as shown in FIG. 2E, anafter-restoration period T3 that is a period lasting up to a prescribedperiod from a time point after the rotation speed of the prime mover 32has been restored to the target rotation speed W2). When an end point ofthe delay period Z14 is set within the after-restoration period T3,operations that are the same as those of S7 and S8 are provided afterS10 shown in FIG. 3A, and the controller 60 switches the travelswitching valve 34 from the first state to the second state in the sameoperation as that of S8. In this case, with regard to the workingmachine 1 in which there is a shift in the speed-change timing resultingfrom variations in a delay in responding to the rotation of hydraulicequipment or the prime mover 32, a speed-change shock when thespeed-increase operation is performed can be suitably reduced. When aspeed-decrease operation is performed, the controller 60 may switch thetravel switching valve 34 from the second state to the first state in anafter-restoration period (for example, as shown in FIG. 2F, anafter-restoration period T13 that is a period lasting up to a prescribedperiod from a time point after the rotation speed of the prime mover 32has been restored to the target rotation speed W2. When an end point ofthe delay period Z15 is set within the after-restoration period T13,operations that are the same as those of S17 and S18 are provided afterS20 shown in FIG. 3B, and the controller 60 switches the travelswitching valve 34 from the second state to the first state in the sameoperation as that of S18. In this case, with regard to the workingmachine 1 in which there is a shift in the speed-change timing resultingfrom variations in a delay in responding to the rotation of hydraulicequipment or the prime mover 32, a speed-change shock occurring when thespeed-decrease operation is performed can be suitably reduced.

A travel detector 67 that is capable of detecting the travel speed ofthe machine body 2 as a travel state is provided. When a speed-increaseoperation is performed or a speed-decrease operation is performed, thecontroller 60 determines the decrease amount of the supply amount to thetravel motors 36 corresponding to the travel speed detected by thetravel detector 67, and decreases the supply amount to the travel motors36 corresponding to the determined decrease amount. According to thisstructure, when a speed-increase operation of the working machine 1 or aspeed-decrease operation of the working machine 1 is performed, thesupply amount to the travel motors 36 is decreased in accordance withthe travel speed, and thus a speed-change shock can be reduced at anytravel speed.

The switching unit is the switch 61 that outputs a speed-changeinstruction to the controller 60. According to this structure, when anoperator or the like operates the switch 61, even if a speed-changeinstruction of increasing speed or decreasing speed has been output tothe controller 60, a speed-change shock can be suitably reduced withregard to the working machine in which there is a shift in thespeed-change timing.

In the Case of Rearward-Movement Speed-Change

Although, in the first embodiment, the case in which there has been aspeed-change instruction during the forward movement of the machine body2 is described, even in the case in which there has been a speed-changeinstruction during rearward movement of the machine body 2, the delayperiod can be changed in the same way. In S51 shown in FIG. 3C and inS61 shown in FIG. 3D, when the operation lever 59 is operated rearwardand the machine body 2 is moving rearward (that is, the rotationdirections of the first travel motor 36L and the second travel motor 36Rare reverse directions as detected by the rotation detection sensor 64),the controller 60 determines whether there has been a speed-increaseinstruction (second-gear instruction) by the switch 61 (S51), anddetermines whether there has been a speed-decrease instruction(first-gear instruction) by the switch 61 (S61). Further, the pressures(the first travel pressure V1 and the third travel pressure V3) detectedby the first travel pressure detectors (the first pressure detector 80 aand the third pressure detector 80 c) are detected with the pressures ofhydraulic fluid that is supplied from the travel pumps 53 to the travelmotors 36 that rotate reversely serving as rearward-movement travelpressures. That is, during the rearward movement, the pressures (thefirst travel pressure V1 and the third travel pressure V3) that aredetected by the first pressure detector 80 a and the third pressuredetector 80 c become rearward-movement travel pressures instead offorward-movement travel pressures, and the pressures (the second travelpressure V2 and the fourth travel pressure V4) detected by the secondpressure detector 80 b and the fourth pressure detector 80 d becomeforward-movement travel pressures instead of rearward-movement travelpressures. According to this structure, in accordance with therearward-movement travel pressures when the working machine 1 movesrearward and a speed-increase operation or a speed-decrease operation isperformed, the controller 60 changes the delay period lasting up to theswitching timing of the travel switching valve 34 from the output timingof the speed-change instruction of increasing speed or decreasing speedat the time of rearward movement. Therefore, with regard to the workingmachine 1 in which there is a shift in the speed-change timing resultingfrom variations in a delay in responding to the rotation of hydraulicequipment or the prime mover 32, a speed-change shock occurring when thespeed is increased or the speed is decreased at the time of the rearwardmovement of the working machine 1 can be reduced.

In a user switching mode in which a user sets a speed-change switchingtiming, when the operation lever 59 (operation member) is operatedrearward and when a speed-decrease operation is performed, thecontroller 60 determines whether the rearward-movement travel pressuresdetected by the first travel pressure detectors exceed a thresholdvalue, and when the controller 60 determines that the threshold value isnot exceeded, the controller 60 causes the central value to be the delayperiod, and when the controller 60 determines that the threshold valueis exceeded, the controller 60 causes the first value to be the delayperiod in place of the central value. According to this structure, inthe user switching mode in which a user sets a speed-change switchingtiming, when the controller 60 determines that the travel pressures whenthe working machine 1 moves rearward and the speed is decreased exceedthe threshold value, the controller 60 changes, as the delay period, theperiod lasting up to the switching timing of the travel switching valve34 from the output timing of the speed-change instruction of decreasingspeed at the time of the rearward movement to the first value that is aperiod shorter than the period indicated by the central value.Therefore, in the user switching mode, with regard to the workingmachine 1 in which there is a shift in the speed-change timing resultingfrom variations in a delay in responding to the rotation of hydraulicequipment or the prime mover 32, a speed-change shock occurring when theworking machine 1 moves rearward can be suitably reduced by changing thedelay period to the first value that is smaller than the central valuewhen the speed-change shock is insufficiently reduced when the centralvalue is used.

When the speed is increased, the controller 60 causes the restorationtime T2 in which the rotation speed of the prime mover is restored to belonger than the decrease time T1 in which the rotation speed of theprime mover is decreased, and when the speed is decreased, thecontroller 60 causes the restoration time T12 to be shorter than thedecrease time T11. According to this structure, after a speed-changeshock has been reduced, the speed-change shock can be made as small aspossible when the rotation speed is to be restored as soon as possiblebefore a speed change.

Second Embodiment

A second embodiment differs from the first embodiment in that acontroller 60 changes a delay period in accordance with a differencebetween a forward-movement travel pressure and a rearward-movementtravel pressure.

When a machine body 2 is moving forward and there has been aspeed-change instruction of increasing speed of decreasing speed, thecontroller 60 changes a delay period in accordance with a differencebetween forward-movement travel pressures (first travel pressure V1 andthird travel pressure V3) detected by first travel pressure detectors(first pressure detector 80 a and third pressure detector 80 c) andrearward-movement travel pressures (second travel pressure V2 and fourthtravel pressure V4) detected by second travel pressure detectors (secondpressure detector 80 b and fourth pressure detector 80 d).

Specifically, in the case of forward-movement speed-increase orforward-movement speed-decrease, when the difference is a positive valueand the absolute value of the difference exceeds a determination value,the controller 60 decreases the delay period. In the case of theforward-movement speed-decrease, when the difference is a negative valueand the absolute value of the difference exceeds a determination value,the controller 60 increases the delay period. In the second embodiment,a memory table TB stores determination values, central values eachindicating a predetermined period from an output timing of aspeed-change instruction of a switch 61, first values each indicating afirst period that is shorter than the period indicated by the centralvalue, and second values each indicating a second period that is longerthan the period indicated by the central value.

Here, an operation of changing a speed-change switching delay period ofthe controller 60 at the time of forward-movement speed-increase in thesecond embodiment is described by using FIG. 3E.

When an operation lever 59 is operated forward and the machine body 2 ismoving forward (that is, when the rotation directions of a first travelmotor 36L and a second travel motor 36R are forward directions asdetected by a rotation detection sensor 64), the controller 60determines whether there has been a speed-increase instruction(second-gear instruction) by the switch 61 (S71). When the controller 60has not received a second-gear instruction (NO in S71), the controller60 returns to S71 and the controller 60 stands by until the controller60 receives a second-gear instruction. On the other hand, when thecontroller 60 has received a second-gear instruction from the switch 61,the controller 60 determines that the speed is to be increased duringthe forward movement (YES in S71), and obtains the rotation speed of aprime mover 32 by using a rotation detector 66 (S72). The controller 60obtains from the memory table TB a determination value corresponding tothe rotation speed of the prime mover 32 (S73).

The controller 60 obtains at least one of the forward-movement travelpressures detected by the first pressure detector 80 a and the thirdpressure detector 80 c (here, the higher of the first travel pressure V1and the third travel pressure V3) and at least one of therearward-movement travel pressures detected by the second pressuredetector 80 b and the fourth pressure detector 80 d (here, the higher ofthe second travel pressure V2 and the fourth travel pressure V4) andcalculates the difference (S74). The controller 60 determines whetherthe difference is positive and the absolute value of the differenceexceeds a determination value (S75). When the difference is positive andthe absolute value of the difference exceeds the determination value(YES in S75), the controller 60 selects the first value that is smallerthan the central value as the delay period (S76). For example, as shownin FIG. 2C and FIG. 2D, the controller 60 changes the delay period fromthe central value (60 milliseconds) to the first value (40milliseconds). On the other hand, when the difference is positive andthe absolute value of the difference does not exceed the determinationvalue (NO in S75), the controller 60 maintains the delay period at thecentral value (60 milliseconds) (S77).

Next, an operation of changing a speed-change switching delay period ofthe controller 60 at the time of forward-movement speed-decrease in thesecond embodiment is described by using FIG. 3F.

When the operation lever 59 is operated forward and the machine body 2is moving forward (that is, when the rotation directions of the firsttravel motor 36L and the second travel motor 36R are forward directionsas detected by the rotation detection sensor 64), the controller 60determines whether there has been a speed-decrease instruction(first-gear instruction) by the switch 61 (S81). When the controller 60has not received a first-gear instruction (NO in S81), the controller 60returns to S81 and the controller 60 stands by until the controller 60receives a first-gear instruction. On the other hand, when thecontroller 60 has received a first-gear instruction from the switch 61,the controller 60 determines that the speed is to be decreased duringthe forward movement (YES in S81), and obtains the rotation speed of theprime mover 32 by using the rotation detector 66 (S82). The controller60 obtains from the memory table TB a determination value correspondingto the rotation speed of the prime mover 32 (S83).

The controller 60 obtains at least one of the forward-movement travelpressures detected by the first pressure detector 80 a and the thirdpressure detector 80 c (here, the higher of the first travel pressure V1and the third travel pressure V3) and at least one of therearward-movement travel pressures detected by the second pressuredetector 80 b and the fourth pressure detector 80 d (here, the higher ofthe second travel pressure V2 and the fourth travel pressure V4), andcalculates the difference (S84). The controller 60 determines whetherthe difference is positive and the absolute value of the differenceexceeds a determination value (S85). When the difference is positive andthe absolute value of the difference exceeds the determination value(YES in S85), the controller 60 selects the first value that is smallerthan the central value as the delay period (S86). For example, as shownin FIG. 2C and FIG. 2D, the controller 60 changes the delay period fromthe central value (680 milliseconds) to the first value (660milliseconds). As shown in FIG. 2B, the delay period Z11 that has beenthe central value (680 milliseconds) is changed to the delay period Z11Bthat is shorter than the delay period Z11.

On the other hand, when the difference is negative or when thedifference is positive and the absolute value of the difference does notexceed the determination value (NO in S85), the controller 60 determineswhether the difference is negative and the absolute value of thedifference exceeds the determination value (S87). When the difference isnegative and the absolute value of the difference does not exceed thedetermination value, or when the difference is positive and the absolutevalue of the difference does not exceed the determination value (NO inS87), the controller 60 maintains the delay period at the central value(680 milliseconds) (S69). As shown in FIG. 2B, the delay period Z11 ismaintained at the central value (680 milliseconds).

On the other hand, when the difference is negative and the absolutevalue of the difference exceeds the determination value (YES in S87),the controller 60 selects the second value that is larger than thecentral value as the delay period (S70). That is, as shown in FIG. 2Cand FIG. 2D, the controller 60 changes the delay period from the centralvalue (680 milliseconds) to the second value (700 milliseconds). Asshown in FIG. 2B, the delay period Z11 that has been the central value(680 milliseconds) is changed to the delay period Z11A that is longerthan the delay period Z11.

In a working machine 1 of the second embodiment above, in accordancewith a difference between a forward-movement travel pressure and arearward-movement travel pressure when the working machine 1 movesforward and a speed-increase operation or a speed-decrease operation isperformed, the controller 60 changes a delay period lasting up to aswitching timing of a travel switching valve 34 from an output timing ofa speed-change instruction of increasing speed of decreasing speed atthe time of the forward movement. Therefore, with regard to the workingmachine 1 in which there is a shift in the speed-change timing resultingfrom variations in a delay in responding to the rotation of hydraulicequipment or the prime mover 32, an adjustment of reducing aspeed-change shock occurring when the speed is increased or decreased atthe time of the forward movement of the working machine 1 can beperformed.

When a difference between a forward-movement travel pressure and arearward-movement travel pressure when the working machine 1 movesforward and a speed-increase operation is performed is a positive valueand the absolute value of the difference exceeds a determination value,the controller 60 decreases the delay period lasting up to the switchingtiming of the travel switching valve 34 from the output timing of thespeed-change instruction of increasing speed at the time of the forwardmovement. Therefore, with regard to the working machine 1 in which thereis a shift in the speed-change timing resulting from variations in adelay in responding to the rotation of hydraulic equipment or the primemover 32, a speed-change shock occurring when the speed is increased atthe time of the forward movement of the working machine 1 can besuitably reduced.

When a difference between a forward-movement travel pressure and arearward-movement travel pressure when the working machine 1 movesforward and the speed is decreased is a positive value and the absolutevalue of the difference exceeds a determination value, the controller 60decreases the delay period lasting up to the switching timing of thetravel switching valve 34 from the output timing of the speed-changeinstruction of decreasing speed at the time of the forward movement.Therefore, with regard to the working machine 1 in which there is ashift in the speed-change timing resulting from variations in a delay inresponding to the rotation of hydraulic equipment or the prime mover 32,a speed-change shock occurring when the speed is decreased at the timeof the forward movement of the working machine 1 can be suitablyreduced.

When a difference between a forward-movement travel pressure and arearward-movement travel pressure when the working machine 1 movesforward and the speed is decreased is a negative value and the absolutevalue of the difference exceeds a determination value, the controller 60increases the delay period lasting up to the switching timing of thetravel switching valve 34 from the output timing of the speed-changeinstruction of decreasing speed at the time of the forward movement.Therefore, with regard to the working machine 1 in which there is ashift in the speed-change timing resulting from variations in a delay inresponding to the rotation of hydraulic equipment or the prime mover 32,a speed-change shock occurring when the speed is decreased at the timeof the forward movement of the working machine 1 can be suitablyreduced.

Third Embodiment

FIG. 6A illustrates a hydraulic system of a working machine 1 accordingto a third embodiment. In the third embodiment, not only can anoperation device 154 change the swash-plate angles of travel pumps 53(first travel pump 53L and second travel pump 53R), but also acontroller 60 is capable of changing the swash-plate angles of thetravel pumps 53.

Note that although FIG. 6A illustrates the travel pumps 53 (the firsttravel pump 53L and the second travel pump 53R), the operation device154, and the controller 60, the other portions are the same as those inFIG. 1 .

The operation device 154 is a joystick device that changes theswash-plate angles of the travel pumps 53 by electricity, and has anoperation lever 59 and an operation detector (sensor 82) that converts,for example, the operation amount and the operation direction of theoperation lever 59 into an electrical signal. When the operation lever59 is operated rightward, leftward, forward, or rearward, the operationdetector 82 detects the operation amount and the operation direction,and the detected operation amount and the detected operation directionare input to the controller 60. The controller 60 changes theswash-plate angles of the travel pumps 53 on the basis of the operationamount and the operation direction detected by the operation detector82. Specifically, the travel pumps 53 (the first travel pump 53L and thesecond travel pump 53R) each have a regulator 155 that changes theswash-plate angle, and the controller 60 controls the regulators 155 tochange the swash-plate angles. With regard to the travel pumps 53 (thefirst travel pump 53L and the second travel pump 53R), as theswash-plate angle increases, the flow rate of hydraulic fluid that isdelivered is increased, and, as the swash-plate angle decreases, theflow rate of hydraulic fluid that is delivered is decreased. An angledetector 68 that detects a swash-plate angle is connected to thecontroller 60. The angle detector 68 allows the controller 60 todetermine the actual swash-plate angles of the travel pumps 53.

When a travel switching valve 34 switches from the first state to thesecond state (when the rotation speeds of the travel motors 36 areincreased from the first speed to the second speed), the controller 60decreases the swash-plate angles of the travel pumps 53 (the firsttravel pump 53L and the second travel pump 53R).

FIG. 4A illustrates the relationship between a swash-plate angle (targetangle, actual angle) when the speed of a travel motor is increased fromthe first speed to the second speed, and switching of the travel motor.

As shown in FIG. 4A, at a time point Q21, it is assumed that a switch 61has been operated and the controller 60 has obtained a speed-increaseinstruction (second-gear instruction) to change from the first state(first speed) to the second state (second speed). When the controller 60obtains a second-gear instruction, the controller 60 decreases an actualangle W11 of each travel pump 53 (the first travel pump 53L and thesecond travel pump 53R) to a prescribed angle W13 that is smaller than aswash-angle target angle (target angle) W12 that has been set on thebasis of the operation amount of the operation device 154. Theprescribed angle W13 is an angle at which a speed-change shock occurringwhen the speed has been switched from the first speed to the secondspeed is reduced, and is a value obtained by subtracting a decreaseamount ΔD2 from the actual angle W11.

As shown in FIG. 9A, the controller 60 stores decrease-amountcalculation data that indicates the relationship between the travelpilot pressure and a decrease amount of the travel pilot pressure (thedecrease amount ΔD2). FIG. 9B is a graph of FIG. 9A. The decrease-amountcalculation data in FIG. 9A and FIG. 9B is only an example and is notlimited thereto. The travel speeds (vehicle speeds) shown in FIG. 9A arevalues shown for explanatory convenience, and are prescribed prime-moverrotation speeds and are not limited thereto.

Although FIG. 9A and FIG. 9B show the decrease amount of the travelpilot pressure, there is a correlation between the decrease amount ofthe travel pilot pressure and the swash-plate angle decrease amount ΔD2.That is, since the structure is configured such that the swash-plateangle is determined by the travel pilot pressure, the higher the travelpilot pressure is, the larger the swash-plate angle is, and the lowerthe travel pilot pressure is, the smaller the swash-plate angle is.

For example, as shown in FIG. 9A, when the controller 60 obtains asecond-gear instruction and the travel speed is 5.0 km/h (travel pilotpressure: 1.5 MPa), the controller 60 sets the decrease amount of thetravel pilot pressure to 0.50 MPa. Note that, as shown in FIG. 9A, whenthe rotation speed of the prime mover is decreased, the controller 60sets a lower limit of the swash-plate angle (the travel pilot pressure)so that the swash-plate angle, that is, the travel pilot pressure doesnot become lower than the minimum pilot pressure.

When, at a time point Q22, the actual angle W11 reaches the prescribedangle W13, the controller 60 restores the actual angle W11 to the targetangle W12. Alternatively, during a decrease time T21 in which the actualangle W11 is decreased to the prescribed angle W13, the controller 60restores the actual angle W11 to the target angle W12. Here, thecontroller 60 causes a restoration time T22 in which the actual angleW11 is restored to the target angle W12 from the prescribed angle W13 tobe longer than the decrease time T21. That is, the controller 60 causesa decrease speed at which the actual angle W11 is decreased to theprescribed angle W13 to be greater than a restoration speed at which theactual angle W11 is restored from the prescribed angle W13 to the targetangle W12.

At a predetermined switching timing from the time point Q21 (a timing inthe restoration time T22 in FIG. 4A), the controller 60 outputs a signalthat energizes a solenoid of the travel switching valve 34 and switchesthe travel switching valve (switching valve) 34 from the first state(the first speed) to the second state (the second speed). In otherwords, the controller 60, after switching the travel switching valve 34to the second state in the restoration time T22, restores the actualangle W11 to the target angle W12.

FIG. 5A is a flowchart of a third operation of the controller 60 whenthe rotation speed of a travel motor is changed from the first speed tothe second speed in the third embodiment. Note that the working machine1 is in a travelling state instead of in a stopped state.

The controller 60 determines whether the switch 61 has been switchedfrom the first speed to the second speed (S21). When the switch 61 hasnot been switched to the second speed, that is, when the switch 61 ismaintained at the first speed (NO in S21), the controller 60 sets theactual angle W11 to the target angle W12 on the basis of the operationof the operation device 154 (S22). When the switch 61 has been switchedfrom the first speed to the second speed (YES in S21), the controller 60determines whether a timing is the predetermined switching timing fromthe time point Q21 (S23). When the timing is not the switching timing(NO in S23), the controller 60 proceeds to S25. On the other hand, whenthe timing is the switching timing (YES in S23), the controller 60switches the travel switching valve 34 from the first state (the firstspeed) to the second state (the second speed) (S24). In the case of NOin S23 or after S24, the controller 60 decreases the actual angle W11 tothe prescribed angle W13 that is smaller than the target angle W12(S25).

The controller 60 determines whether the actual angle W11 has reachedthe prescribed angle W13 (S26), and when the actual angle W1 has notreached the prescribed angle W13 (NO in S26), the controller 60 returnsto S23. On the other hand, when the controller 60 determines that theactual angle W11 has reached the prescribed angle W13 (YES in S26), thecontroller 60 determines whether a timing is the switching timing (S27).When the timing is the switching timing (YES in S27), the controller 60switches the travel switching valve 34 from the first state (the firstspeed) to the second state (second speed) (S28). On the other hand, whenthe timing is not the switching timing (NO in S27) or after S28, thecontroller 60 restores the actual angle W11 to the target angle W12(S29). The controller 60 determines whether the actual angle W11 hasbeen restored to the target angle W12 (S30), and when the controller 60determines that the actual angle W11 has not been restored (NO in S30),the controller 60 returns to S27. Note that when the controller 60determines that the actual angle W11 has been restored to the targetangle W12 (YES in S30), the process ends.

FIG. 4B illustrates the relationship between a swash-plate angle (targetangle, actual angle) when the speed of a travel motor is decreased fromthe second speed to the first speed, and switching of the travel motor.

As shown in FIG. 4B, at a time point Q31, it is assumed that the switch61 has been operated and the controller 60 has obtained a speed-decreaseinstruction (first-gear instruction) to change from the second state(second speed) to the first state (first speed). When the controller 60obtains a first-gear instruction, the controller 60 decreases the actualangle W11 of the travel pumps 53 (the first travel pump 53L and thesecond travel pump 53R) to a prescribed angle W13 that is smaller thanthe swash-plate-angle target angle W12 that has been set on the basis ofthe operation amount of the operation device 154.

When, at a time point Q32, the actual angle W11 reaches the prescribedangle W13, the controller 60 restores the actual angle W11 to the targetangle W12. Alternatively, during a decrease time T31 in which the actualangle W11 is decreased to the prescribed angle W13, the controller 60restores the actual angle W11 to the target angle W12. Here, thecontroller 60 causes a restoration time T32 in which the actual angleW11 is restored to the target angle W12 from the prescribed angle W13 tobe shorter than the decrease time T31. That is, the controller 60 causesa decrease speed at which the actual angle W11 is decreased to theprescribed angle W13 to be less than a restoration speed at which theactual angle W11 is restored to the target angle W12 from the prescribedangle W13.

At a predetermined switching timing from the time point Q31 (forexample, a timing in the decrease time T31), the controller 60 outputs asignal that energizes the solenoid of the travel switching valve 34 andswitches the travel switching valve 34 from the second state (the secondspeed) to the first state (the first speed). In other words, thecontroller 60 restores the actual angle W11 to the target angle W12during the decrease time T31.

FIG. 5B is a flowchart of a fourth operation of the controller 60 whenthe rotation speed of a travel motor is changed from the second speed tothe first speed in the third embodiment. Note that the working machine 1is in a travelling state instead of in a stopped state.

The controller 60 determines whether the switch 61 has been switchedfrom the second speed to the first speed (S31). When the switch 61 hasnot been switched to the first speed, that is, when the switch 61 ismaintained at the second speed (NO in S31), the controller 60 sets theactual angle W11 to the target angle W12 on the basis of the operationof the operation device 154 (S32). When the switch 61 has been switchedfrom the second speed to the first speed (YES in S31), the controller 60determines whether a timing is a predetermined switching timing from thetime point Q31 (S33). When the timing is not the switching timing (NO inS33), the controller 60 proceeds to S35. On the other hand, when thetiming is the switching timing (YES in S33), the controller 60 switchesthe travel switching valve 34 from the second state (the second speed)to the first state (the first speed) (S34). In the case of NO in S33 orafter S34, the controller 60 decreases the actual angle W11 to theprescribed angle W13 that is lower than the target angle W12 (S35). Thecontroller 60 determines whether the actual angle W11 has reached theprescribed angle W13 (S36), and when the actual angle W1 has not reachedthe prescribed angle W13 (NO in S36), the controller returns to S33. Onthe other hand, when the actual angle W11 has reached the prescribedangle W13 (YES in S36), the controller 60 determines whether a timing isthe switching timing (S37). When the timing is the switching timing (YESin S37), the controller 60 switches the travel switching valve 34 fromthe second state (the second speed) to the first state (first speed)(S38). On the other hand, when the timing is not the switching timing(NO in S37) or after S38, the controller 60 restores the actual angleW11 to the target angle W12 (S39). The controller 60 determines whetherthe actual angle W11 has been restored to the target angle W12 (S40),and when the controller 60 determines that the actual angle W11 has notbeen restored (NO in S40), the controller 60 returns to S37. Note thatwhen the controller 60 determines that the actual angle W11 has beenrestored to the target angle W12 (YES in S40), the process ends.

Even in the working machine 1 of the third embodiment, the controller 60changes a delay period lasting up to the switching timing of the travelswitching valve 34 from an output timing of a speed-change instructionof the switching unit (the switch 61) in accordance with the travelpressures detected by the pressure detectors 80 (travel pressuredetectors) at the time of a speed-change instruction. Since the changingof the delay period is the same as those in the first and secondembodiments above, the changing of the delay period is not describedhere.

For example, when illustrating this using FIG. 3C of the firstembodiment, when a forward-movement travel pressure exceeds thespeed-increase first threshold value (YES in S55), the controller 60selects, as a delay period, the first value that is smaller than thecentral value (S56). That is, as shown in FIG. 2C and FIG. 2D, thecontroller 60 changes the delay period from the central value (60milliseconds) to the first value (40 milliseconds). As shown in FIG. 4A,a delay period Z12 that has been the central value (60 milliseconds) ischanged to a delay period Z12A that is shorter than the delay periodZ12. On the other hand, when the forward-movement travel pressure doesnot exceed the speed-increase first threshold value (NO in S55), asshown in FIG. 2C and FIG. 2D, the controller 60 maintains the delayperiod at the central value (60 milliseconds) (S57). As shown in FIG.4A, the delay period Z12 is maintained at the central value (60milliseconds).

When illustrating this using FIG. 3D of the first embodiment, when arearward-movement travel pressure exceeds the speed-decrease secondthreshold value (YES in S68), the controller 60 selects, as a delayperiod, the second value that is larger than the central value (S70).That is, as shown in FIG. 2C and FIG. 2D, the controller 60 changes thedelay period from the central value (680 milliseconds) to the secondvalue (700 milliseconds). As shown in FIG. 4B, a delay period Z13 thathas been the central value (680 milliseconds) is changed to a delayperiod Z13A that is longer than the delay period Z13.

Even the working machine 1 of the third embodiment is capable ofproviding the same effects as those of the working machines 1 of thefirst and second embodiments above.

Fourth Embodiment

Although, in the embodiment described above, the swash-plate angle ischanged by the regulator 155, the swash-plate angle may be changed byanother method. For example, as shown in FIG. 7A, a delivery fluidpassage 40 is a branched passage that branches off in the middle, and aproportional valve 69 is connected to a section 40 a extending to atravel operation device 54. The proportional valve 69 is anelectromagnetic proportional valve and its opening can be changed bycontrol of a controller 60.

In a state in which an operation lever 59 of the travel operation device54 is in full stroke, that is, operation valves 55 (55A, 55B, 55C, 55D)are substantially fully open, when the controller 60 has obtained aninstruction of switching from a first gear state to a second gear stateby a switch 61, the controller 60, by making the opening of theproportional valve 69 smaller than the opening when the switch 61 isbeing operated, decreases a primary pressure of a hydraulic fluidflowing toward the operation valves 55 and, as in FIG. 4A, causes theswash-plate angles of travel pumps 53 (first travel pump 53L and secondtravel pump 53R) to be smaller than the present swash-plate angles.After decreasing the swash-plate angles of the travel pumps 53 (thefirst travel pump 53L and the second travel pump 53R), the controller 60switches a travel switching valve 34 to the second state and, afterswitching the travel switching valve 34 to the second state, restoresthe opening of the proportional valve 69.

In a state in which the operation lever 59 of the travel operationdevice 54 is in full stroke, when the controller 60 has obtained aninstruction of switching from the second gear state to the first gearstate by the switch 61, the controller 60, by making the opening of theproportional valve 69 smaller than the opening when the switch 61 isbeing operated, decreases a primary pressure of a hydraulic fluidflowing toward the operation valves 55 and, as in FIG. 4B, causes theswash-plate angles of the travel pumps 53 (the first travel pump 53L andthe second travel pump 53R) to be smaller than the present swash-plateangles. After decreasing the swash-plate angles of the travel pumps 53(the first travel pump 53L and the second travel pump 53R), thecontroller 60 switches the travel switching valve 34 to the first stateand, after switching the travel switching valve 34 to the first state,restores the opening of the proportional valve 69. Note that whether theoperation lever 59 is in full stroke can be determined by the operationamount detected by an operation detector (sensor) 82.

That is, as shown in FIG. 7A, even by using the proportional valve 69provided in the delivery flow passage 40 (40 a), when the speed isincreased or decreased, the swash-plate angles of the travel pumps 53(the first travel pump 53L and the second travel pump 53R) can bedecreased.

Even in the working machine 1 of the fourth embodiment, in accordancewith the travel pressures detected by pressure detectors 80 (travelpressure detectors) at the time of a speed-change instruction, thecontroller 60 changes a delay period lasting up to a switching timing ofthe travel switching valve 34 from an output timing of a speed-changeinstruction of the switching unit (the switch 61). Since the changing ofthe delay period is the same as those in the first and secondembodiments above, the changing of the delay period is not describedhere.

Even the working machine 1 of the fourth embodiment is capable ofproviding the same effects as those of the working machines 1 of thefirst and second embodiments above.

When a speed-change instruction of increasing speed is issued byoperating the switch 61 (switching unit), for example, in a restorationperiod in which the opening of the proportional valve 69 (actuatingvalve) after being decreased is restored (for example, the period of therestoration time T22 shown in FIG. 4A), the controller 60 switches thetravel switching valve 34 from the first state to the second state inaccordance with the speed-change instruction. Therefore, when aspeed-increase operation is performed, the switching timing of thetravel switching valve 34 during control of decreasing the opening ofthe proportional valve 69 can be made into a suitable timing.Consequently, with regard to the working machine 1 in which there is ashift in the speed-change timing resulting from variations in a delay inresponding to the rotation of hydraulic equipment or a prime mover 32, aspeed-change shock occurring when the speed of the working machine 1 isincreased can be reduced.

When a speed-change instruction of decreasing speed is issued byoperating the switch 61 (switching unit), in a decrease period in whichthe opening of the proportional valve 69 (actuating valve) is decreased,the controller 60 switches the travel switching valve 34 from the secondstate to the first state. Therefore, when a speed-decrease operation isperformed, the switching timing of the travel switching valve 34 duringcontrol of decreasing the opening of the proportional valve 69 can bemade into a suitable timing. Consequently, with regard to the workingmachine 1 in which there is a shift in the speed-change timing resultingfrom variations in a delay in responding to the rotation of hydraulicequipment or the prime mover 32, a speed-change shock occurring when thespeed of the working machine 1 is decreased can be reduced.

As described above, the controller 60 is capable of changing the delayperiod lasting up to the switching timing of the travel switching valve34 from the output timing of the speed-change instruction of the switch61 in accordance with the travel pressures detected by pressuredetectors 80 (travel pressure detectors) at the time of a speed-changeinstruction. Therefore, the controller 60 is capable of changing thedelay period to a prior period shown in FIG. 4E and FIG. 4F or anafter-restoration period shown in FIG. 4C and FIG. 4D.

Here, the case in which delay periods Z16A and Z17A are set at the priorperiods shown in FIG. 4E and FIG. 4F is described. When a speed-increaseoperation is performed, the controller 60 may switch the travelswitching valve 34 from the first state to the second state in a priorperiod lasting up to when the supply amount to travel motors 36 startsdecreasing (for example, as shown in FIG. 4E, a prior period T21A up towhen the opening of the proportional valve 69 (actuating valve) startsdecreasing). When the controller 60 sets the delay period Z16A withinthe prior period T21A, the controller 60 switches the travel switchingvalve 34 from the second state to the first state in S24 shown in FIG.5A. In this case, with regard to the working machine 1 in which there isa shift in the speed-change timing resulting from variations in a delayin responding to the rotation of hydraulic equipment or the prime mover32, a speed-change shock occurring when the speed-increase operation isperformed can be suitably reduced. When a speed-decrease operation isperformed, the controller 60 may switch the travel switching valve 34from the second state to the first state in a prior period lasting up towhen the supply amount to the travel motors 36 starts decreasing (forexample, as shown in FIG. 4F, a prior period T31A up to when the openingof the proportional valve 69 (actuating valve) starts decreasing). Whenthe controller 60 sets the delay period Z17A within the prior periodT31A, the controller 60 switches the travel switching valve 34 from thesecond state to the first state in S34 shown in FIG. 5B. In this case,with regard to the working machine 1 in which there is a shift in thespeed-change timing resulting from variations in a delay in respondingto the rotation of hydraulic equipment or the prime mover 32, aspeed-change shock occurring when the speed-decrease operation isperformed can be suitably reduced.

Next, the case in which delay periods Z16 and Z17 are set atafter-restoration periods shown in FIG. 4C and FIG. 4D is described.When a speed-increase operation is performed, the controller 60 mayswitch the travel switching valve 34 from the first state to the secondstate in an after-restoration period (for example, as shown in FIG. 4C,an after-restoration period T23 that is a period up to a prescribedperiod from a time point when the opening of the proportional valve 69(actuating valve) has been restored. When an end point of the delayperiod Z16 is set within the after-restoration period T23, operationsthat are the same as those of S27 and S28 are provided after S30 shownin FIG. 5A, and the controller 60 switches the travel switching valve 34from the first state to the second state in the same operation as thatof S28. In this case, with regard to the working machine 1 in whichthere is a shift in the speed-change timing resulting from variations ina delay in responding to the rotation of hydraulic equipment or theprime mover 32, a speed-change shock occurring when the speed-increaseoperation is performed can be suitably reduced. When a speed-decreaseoperation is performed, the controller 60 may switch the travelswitching valve 34 from the second state to the first state in anafter-restoration period (for example, as shown in FIG. 4D, anafter-restoration period T33 that is a period up to a prescribed periodfrom a time point when the opening of the proportional valve 69(actuating valve) has been restored. When an end point of the delayperiod Z17 is set within the after-restoration period T33, operationsthat are the same as those of S37 and S38 are provided after S40 shownin FIG. 5B, and the controller 60 switches the travel switching valve 34from the second state to the first state in the same operation as thatof S38. In this case, with regard to the working machine 1 in whichthere is a shift in the speed-change timing resulting from variations ina delay in responding to the rotation of hydraulic equipment or theprime mover 32, a speed-change shock occurring when the speed-decreaseoperation is performed can be suitably reduced.

When a speed-increase operation is performed, the controller 60 causesthe absolute value of the gradient of the supply amount to the operationvalves 55 to be smaller in the restoration period (for example, theperiod of the restoration time T22 shown in FIG. 4A) than in thedecrease period (for example, the period of the decrease time T21 shownin FIG. 4A). According to this structure, it is possible to decrease aperiod for reducing a speed-change shock while reducing the speed-changeshock. Specifically, when a speed-increase operation is performed, theabsolute value of the gradient of the supply amount to the operationvalves 55 is made smaller in the restoration period than in the decreaseperiod. That is, since the decrease period is shorter than therestoration period, the period for reducing a speed-change shock can becorrespondingly shortened.

When a speed-decrease operation is performed, the controller 60 causesthe absolute value of the gradient of the supply amount to the operationvalves 55 to be smaller in the decrease period (for example, the periodof the decrease time T31 shown in FIG. 4B) than in the restorationperiod (for example, the period of a restoration time T32 shown in FIG.4B). According to this structure, it is possible to decrease a periodfor reducing a speed-change shock while reducing the speed-change shock.Specifically, when a speed-decrease operation is performed, the absolutevalue of the gradient of the supply amount to the operation valves 55 ismade smaller in the decrease period than in the restoration period. Thatis, since the restoration period is shorter than the decrease period,the period for reducing a speed-change shock can be correspondinglyshortened.

Fifth Embodiment

A working machine 1 of a fifth embodiment shown in FIG. 7B includes agradient detector 63 (for example, an acceleration sensor or an inertialmeasurement sensor) that detects the pitch angle of a machine body 2.When the machine body 2 moves forward or rearward in an ordinary modethat is not a setting mode of setting a speed-change switching timing,if the pitch angle detected by the gradient detector 63 is a positivevalue, a controller 60 corrects a delay period so that the delay periodis decreased in accordance with the magnitude of the pitch angle, and,if the pitch angle detected by the gradient detector 63 is a negativevalue, the controller 60 corrects the delay period so that the delayperiod is increased in accordance with the magnitude of the pitch angle.

According to this structure, since the delay period is corrected inaccordance with the pitch angle, a speed-change shock occurring when theworking machine 1 moves forward or rearward on a rising slope or adescending slope in the ordinary mode can be suitably reduced.

Further, when the machine body 2 moves forward or rearward in thesetting mode, if the pitch angle detected by the gradient detector 63 isa positive value, the controller 60 may correct a threshold value sothat the threshold value is increased in accordance with the magnitudeof the pitch angle, and, if the pitch angle detected by the gradientdetector 63 is a negative value, the controller 60 may correct thethreshold value so that the threshold value is decreased in accordancewith the magnitude of the pitch angle. According to this structure,since the travel pressure is increased at the rising slope, when thethreshold value is increased in accordance with the increase of thetravel pressure, even if the setting mode of setting the speed-changeswitching timing is realized at the rising slope, the delay period canbe suitably set. In addition, since the travel pressure is decreased atthe descending slope, when the threshold value is decreased inaccordance with the decrease of the travel pressure, even if the settingmode of setting the speed-change switching timing is realized at thedescending slope, the delay period can be suitably set.

Modification 1

In the user switching mode in which a user sets a speed-change switchingtiming, when the operation lever 59 (operation member) is operatedforward and when a speed-increase operation or a speed-decreaseoperation is performed, the controller 60 determines whetherforward-movement travel pressures (that is, the first travel pressure V1and the third travel pressure V3) detected by the first travel pressuredetectors (the first pressure detector 80 a and the third pressuredetector 80 c) exceed a threshold value, and when the controller 60determines that the threshold value is not exceeded, the controller 60causes the central value to be a delay period, and when the controller60 determines that the threshold value is exceeded, the controller 60causes the first value to be the delay period in place of the centralvalue. According to this structure, in the user switching mode in whicha user sets a speed-change switching timing, when the controller 60determines that the forward-movement travel pressures when the workingmachine 1 moves forward and the speed-increase operation or thespeed-decrease operation is performed exceed the threshold value, thecontroller 60 changes, as the delay period, the period lasting up to theswitching timing of the travel switching valve 34 from the output timingof the speed-change instruction of increasing or decreasing speed at thetime of the forward movement to the first value that is a period shorterthan the period indicated by the central value. Therefore, in the userswitching mode, with regard to the working machine 1 in which there is ashift in the speed-change timing resulting from variations in a delay inresponding to the rotation of hydraulic equipment or the prime mover 32,a speed-change shock occurring when the working machine 1 moves forwardcan be suitably reduced by changing the delay period to the first valuethat is smaller than the central value when the speed-change shock isinsufficiently reduced when the central value is used.

Note that, although, in FIG. 2C and FIG. 2D, there is only one value forthe first value when the speed is increased (for example, 40milliseconds) and for the second value when the speed is increased (forexample, 80 milliseconds) and there is only one value for the firstvalue when the speed is decreased (for example, 660 milliseconds) andfor the second value when the speed is decreased (for example, 700milliseconds), the number of values is not limited thereto. For example,the number of first values when the speed is increased may be aplurality of values, such as 50 milliseconds, 40 milliseconds, and 30milliseconds, and the number of second values when the speed isincreased may be a plurality of values, such as 70 milliseconds, 80milliseconds, and 90 milliseconds; and, until the travel pressuresdetected by the pressure detectors 80 no longer exceed the thresholdvalue, the controller 60 may select the first value in a graduallydecreasing order, and may select the second value in a graduallyincreasing order. The number of first values when the speed is decreased(for example, 660 milliseconds) and the number of second values when thespeed is decreased (for example, 700 milliseconds) may each be aplurality of values. For example, the number of first values when thespeed is decreased may be a plurality of values, such as 670milliseconds, 660 milliseconds, and 650 milliseconds, and the number ofsecond values when the speed is decreased may be a plurality of values,such as 690 milliseconds, 700 milliseconds, and 710 milliseconds; and,until the travel pressures detected by the pressure detectors 80 nolonger exceed the threshold value, the controller 60 may select thefirst value in a gradually decreasing order, and may select the secondvalue in a gradually increasing order.

Modification 2

In Modification 2, a delay period at the time of forward movement isinternally changed on the basis of operation performance. Specifically,in the ordinary mode that is not the setting mode of setting aspeed-change switching timing, when the operation lever 59 (operationmember) is operated forward and a speed-increase operation or aspeed-decrease operation is performed, the controller 60 determineswhether forward-movement travel pressures detected by the first travelpressure detectors exceed a threshold value. When the controller 60determines that the threshold value is exceeded, the controller 60 maystore in the memory 60 a a determination result that the threshold valueis exceeded, and when the number of the determination result reaches apredetermined performance number, the controller 60 may cause the firstvalue to be the delay period in place of the central value.

According to this structure, in the ordinary mode that is not thesetting mode, when the determination result in which theforward-movement travel pressures when the working machine 1 movesforward and a speed-increase operation or a speed-decrease operation isperformed are determined as exceeding the threshold value reaches thepredetermined performance number, the delay period is changed to thefirst value in place of the central value. Therefore, with regard to theworking machine 1 in which there is a shift in the speed-change timingresulting from variations in a delay in responding to the rotation ofhydraulic equipment or the prime mover 32, the delay period can bechanged to the first value that is smaller than the central value on thebasis of a performance result that a speed-change shock isinsufficiently reduced when the central value is used. Consequently, thespeed-change shock occurring when the working machine 1 moves forwardcan be suitably reduced on the basis of the performance result.

Further, a delay period at the time of rearward movement may beinternally changed on the basis of operation performance. Specifically,in the ordinary mode that is not the setting mode of setting aspeed-change switching timing, when the operation lever 59 (operationmember) is operated rearward and a speed-decrease operation isperformed, the controller 60 determines whether rearward-movement travelpressures detected by the first travel pressure detectors exceed athreshold value. When the controller 60 determines that the thresholdvalue is exceeded, the controller 60 may store in the memory 60 a adetermination result that the threshold value is exceeded; and when thenumber of the determination result does not reach a predeterminedperformance number, the controller 60 may cause the central value to bethe delay period, and when the number of the determination result hasreached the predetermined performance number, the controller 60 maycause the first value to be the delay period.

According to this structure, in the ordinary mode that is not thesetting mode, when the determination result in which therearward-movement travel pressures when the working machine 1 movesrearward and a speed-decrease operation is performed are determined asexceeding the threshold value reaches the predetermined performancenumber, the delay period is changed to the first value in place of thecentral value. Therefore, with regard to the working machine 1 in whichthere is a shift in the speed-change timing resulting from variations ina delay in responding to the rotation of hydraulic equipment or theprime mover 32, the delay period can be changed to the first value thatis smaller than the central value on the basis of a performance resultthat a speed-change shock is insufficiently reduced when the centralvalue is used. Consequently, the speed-change shock occurring when theworking machine 1 moves rearward can be suitably reduced on the basis ofthe performance result.

Modification 3

In a working machine 1 of Modification 3, when a speed-changeinstruction of increasing speed is issued by operating the switch 61,the controller 60 switches the travel switching valve 34 from the firststate to the second state in accordance with the speed-changeinstruction in the prior period lasting up to when the opening of theproportional valve (actuating valve) 69 starts decreasing, therestoration period in which the opening of the proportional valve 69after being decreased is restored, or the after-restoration period; andwhen a speed-change instruction of decreasing speed is issued byoperating the switch 61, the controller 60 switches the travel switchingvalve 34 from the first state to the second state in accordance with thespeed-change instruction in the prior period lasting up to when therotation speed of the prime mover 32 starts decreasing, in the decreaseperiod in which the rotation speed of the prime mover 32 is decreased toa value lower than the target rotation speed determined by operating theaccelerator 65, or in the after-restoration period.

According to this structure, when a speed-increase operation isperformed, the controller 60 switches the travel switching valve 34 fromthe first state to the second state in the prior period lasting up towhen the opening of the proportional valve 69 starts decreasing, therestoration period in which the opening of the proportional valve 69 isrestored, or in the after-restoration period. Therefore, when thespeed-increase operation is performed, the switching timing of thetravel switching valve 34 during control of decreasing the opening ofthe proportional valve 69 can be made into a suitable timing.Consequently, with regard to the working machine 1 in which there is ashift in the speed-change timing resulting from variations in a delay inresponding to the rotation of hydraulic equipment or a prime mover 32, aspeed-change shock occurring when the speed of the working machine 1 isincreased can be suitably reduced. When a speed-decrease operation isperformed, the controller 60 switches the travel switching valve fromthe second state to the first state in the prior period lasting up towhen the rotation speed of the prime mover 32 starts decreasing, in thedecrease period in which the rotation speed of the prime mover 32 isdecreased, or in the after-restoration period. Therefore, when thespeed-decrease operation is performed, the switching timing of thetravel switching valve 34 during control of decreasing the rotationspeed of the prime mover 32 can be made into a suitable timing.Consequently, with regard to the working machine 1 in which there is ashift in the speed-change timing resulting from variations in a delay inresponding to the rotation of hydraulic equipment or the prime mover 32,a speed-change shock occurring when the speed of the working machine 1is decreased can be suitably reduced.

Modification 4

Although, in, for example, the first and fourth embodiments describedabove, the travel operation device 54 is a hydraulic type that changesthe pilot pressure that acts on the travel pumps (the first travel pump53L and the second travel pump 53R) by the operation valves 55, in aworking machine of Modification 4, a travel operation device 54 shown inFIG. 6B may be a device that operates electrically.

As shown in FIG. 6B, the travel operation device 54 includes anoperation lever 59 that swings in a left-right direction (machine-bodywidth direction) or a front-rear direction, and operation valves(operation valves 55 a, 55 b, 55 c, and 55 d) that are each formed froman electromagnetic proportional valve. An operation detection sensorthat detects the operation amount and the operation direction of theoperation lever 59 is connected to the controller 60. The controller 60controls the operation valves 55 (the operation valves 55 a, 55 b, 55 c,and 55 d) on the basis of the operation amount and the operationdirection detected by the operation detection sensor.

When the operation lever 59 is operated forward (direction of arrow A1;see FIG. 1 ), the controller 60 outputs a control signal to theoperation valve 55 a and the operation valve 55 c, and causes swashplates of the first travel pump 53L and the second travel pump 53R toswing in a forward rotation (forward movement) direction.

When the operation lever 59 is operated rearward (direction of arrow A2;see FIG. 1 ), the controller 60 outputs a control signal to theoperation valve 55 b and the operation valve 55 d, and causes swashplates of the first travel pump 53L and the second travel pump 53R toswing in a reverse rotation (rearward movement) direction.

When the operation lever 59 is operated rightward (direction of arrowA3; see FIG. 1 ), the controller 60 outputs a control signal to theoperation valve 55 a and the operation valve 55 d, and causes the swashplate of the first travel pump 53L to swing in the forward rotationdirection and the swash plate of the second travel pump 53R to swing inthe reverse rotation direction.

When the operation lever 59 is operated leftward (direction of arrow A4;see FIG. 1 ), the controller 60 outputs a control signal to theoperation valve 55 b and the operation valve 55 c, and causes the swashplate of the first travel pump 53L to swing in the reverse rotationdirection and the swash plate of the second travel pump 53R to swing inthe forward rotation direction.

Even in the structure shown in FIG. 6B, the controller 60 may change thedelay period lasting up to the switching timing of the travel switchingvalve 34 from the output timing of a speed-change instruction of theswitch 61. Therefore, with regard to the working machine 1 in whichthere is a shift in the speed-change timing resulting from variations ina delay in responding to the rotation of hydraulic equipment or theprime mover 32, an adjustment of reducing a speed-change shock can beperformed.

Modification 5

FIG. 6C illustrates part of a hydraulic system (hydraulic circuit) of aworking machine in Modification 5. As in FIG. 6B, in Modification 5, anoperation lever 59 including a joystick that operates electrically, anda controller 60 are used. In the present modification, instead of theoperation valves 55 (the operation valves 55 a, 55 b, 55 c, and 55 d)shown in FIG. 6B, operation valves (actuating valves) 155L and 155R thatare formed from electromagnetic proportional valves shown in FIG. 6C,and hydraulic regulators 156L and 156R are used.

As in Modification 4, the operation lever 59 is an operation lever thatswings in a left-right direction (machine-body width direction) or afront-rear direction. The operation lever 59 has a sensor (operationdetection sensor) that detects the operation amount (swing amount) andthe operation direction (swing direction). The operation detectionsensor is connected to the controller 60.

The operation valves (actuating valves) 155L and 155R that are formedfrom electromagnetic proportional valves are electrically connected tothe controller 60. As with the operation valves 55 (the operation valves55 a, 55 b, 55 c, and 55 d) according to Modification 4, even in theoperation valves 155L and 155R, the switching positions and openings ofthe valves are controlled by a control signal from the controller 60that is in accordance with the operation of the operation lever 59.

As shown in FIG. 6C, the hydraulic regulators 156L and 156R areconnected to the swash plates of the travel pumps (the first travel pump53L and the second travel pump 53R). The hydraulic regulators 156L and156R are capable of changing the angles of the swash plates (swash-plateangles) of the travel pumps 53L and 53R (the first travel pump 53L andthe second travel pump 53R), and each include a supply chamber 157 towhich hydraulic fluid is supplied and a piston rod 158 that is providedat the supply chamber 157. Each piston rod 158 is connected to thecorresponding swash plate, and due to the movement (that is, extensionand compression) of the corresponding piston rod 158, the correspondingswash plate swings to make it possible to change the swash-plate angle.

Here, the supply chamber 157 of the hydraulic regulator 156L that isconnected to the swash plate of the first travel pump 53L is called afirst pressure receiver. The supply chamber 157 of the hydraulicregulator 156R that is connected to the swash plate of the second travelpump 53R is called a second pressure receiver.

The operation valve 155L is a valve that operates the hydraulicregulator 156L, and is a valve that controls the amount of hydraulicfluid that is output by the first travel pump 53L by operating thehydraulic regulator 156L. The operation valve 155L is formed from anelectromagnetic proportional valve having a solenoid 160L, and a spoolof the operation valve 155L moves on the basis of a control signal thathas been output from the controller 60 to the solenoid 160L. Themovement of the spool changes the opening of the operation valve 155L.The operation valve 155L has a first position 159 a, a second position159 b, and a neutral position 159 c, and is switchable to any one ofthese positions.

A first port of the operation valve 155L and the supply chamber 157 ofthe hydraulic regulator 156L are connected to each other by a firsttravel fluid passage 45 a. A second port of the operation valve 155L andthe supply chamber 157 of the hydraulic regulator 156L are connected toeach other by a second travel fluid passage 45 b.

The operation valve 155R is a valve that operates the hydraulicregulator 156R, and is a valve that controls the amount of hydraulicfluid that is output by the second travel pump 53R by operating thehydraulic regulator 156R. The operation valve 155R is formed from anelectromagnetic proportional valve having a solenoid 160R, and a spoolof the operation valve 155R moves on the basis of a control signal thathas been provided from the controller 60 to the solenoid 160R. Themovement of the spool changes the opening of the operation valve 155R.The operation valve 155R has a first position 159 a, a second position159 b, and a neutral position 159 c, and is switchable to any one ofthese positions.

A first port of the operation valve 155R and the supply chamber 157 ofthe hydraulic regulator 156R are connected to each other by a thirdtravel fluid passage 45 c. A second port of the operation valve 155R andthe supply chamber 157 of the hydraulic regulator 156R are connected toeach other by a fourth travel fluid passage 45 d.

If the operation valve 155L and the operation valve 155R are eachswitched to the first position 159 a, the hydraulic regulators 156L and156R operate to swing the swash plate of the first travel pump 53L andthe swash plate of the second travel pump 53R, as a result of which thetravel pumps rotate forward. If the operation valve 155L and theoperation valve 155R are each switched to the second position 159 b, thehydraulic regulators 156L and 156R operate to swing the swash plate ofthe first travel pump 53L and the swash plate of the second travel pump53R, as a result of which the travel pumps rotate reversely.

If the operation valve 155L is switched to the first position 159 a andthe operation valve 155R is switched to the second position 159 b, thefirst travel pump 53L rotates forward and the second travel pump 53Rrotates reversely. If the operation valve 155L is switched to the secondposition 159 b and the operation valve 155R is switched to the firstposition 159 a, the first travel pump 53L rotates reversely and thesecond travel pump 53R rotates forward.

In the present modification, by using the operation lever 59 and thecontroller 60, the operation valve 155L and the operation valve 155R areoperated to operate the hydraulic regulator 156L and the hydraulicregulator 156R, as a result of which, as in the second embodiment, theswash plate of the first travel pump 53L and the swash plate of thesecond travel pump 53R are swung.

Even in the structure shown in FIG. 6C, the controller 60 may change thedelay period lasting up to the switching timing of the travel switchingvalve 34 from the output timing of a speed-change instruction of theswitch 61. Therefore, with regard to the working machine 1 in whichthere is a shift in the speed-change timing resulting from variations ina delay in responding to the rotation of hydraulic equipment or theprime mover 32, an adjustment of reducing a speed-change shock can beperformed.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

Although, in the embodiments described above, the switching unit (switch61) is a switch 61 that can be operated, for example, manually by anoperator or the like, the switching unit may be built in the controller60. When the switching unit is built in the controller 60, the switchingunit includes a program stored in the controller 60, an electricalcomponent, and an electronic component (electrical circuit andelectronic circuit). In this case, the switching unit of the controller60 determines whether to switch to the first gear state and the secondgear state on the basis of detection information from various detectorsof the working machine 1, such as a sensor, and a control signal isoutput to the travel switching valve 34 on the basis of a determinationresult. When the travel switching valve 34 has obtained a control signalfor the first gear state, the travel switching valve 34 is switched tothe first gear state, and when the travel switching valve 34 hasobtained a control signal for the second gear state, the travelswitching valve 34 is switched to the second gear state.

The travel switching valve 34 is to be a valve that is switchable to thefirst state in which the travel motors 36 (the first travel motor 36Land the second travel motor 36R) are caused to be in the first speed andthat is switchable to the second state in which the travel motors 36 arecaused to be in the second speed, and may be a proportional valvediffering from a directional switching valve.

The travel motors 36 may be motors having a neutral between the firstgear and the second gear.

The travel motors 36 (the first travel motor 36L and the second travelmotor 36R) may be axial piston motors or radial piston motors. When thetravel motors are radial piston gears, due to the motor capacity beingincreased, the travel motors 36 can be switched to the first gear, and,due to the motor capacity being decreased, the travel motors 36 can beswitched to the second gear.

Since the travel speed changes by operating the operation lever 59, thetravel detector 67 may be a device that detects the travel speed on thebasis of the operation amount (operation angle) and the operationposition of the operation lever 59. As described above, since the secondgear (the second state) is to be higher than the first gear (the firststate), the shift stages of the working machine are not limited to twostages and may be many stages (a plurality of stages).

What is claimed is:
 1. A working machine, comprising: a prime mover; atravel pump driven by power of the prime mover to deliver a hydraulicfluid; a travel motor rotated by the hydraulic fluid delivered by thetravel pump; a machine body where the prime mover, the travel pump, andthe travel motor are provided; a travel switching valve switchable to afirst state in which a rotation speed of the travel motor is capable ofbeing increased up to a first maximum speed, and to a second state inwhich the rotation speed of the travel motor is capable of beingincreased up to a second maximum speed that is greater than the firstmaximum speed; a travel operation device including an operation valveoperable to change a pressure of a hydraulic fluid to operate the travelpump in accordance with an operation of an operation member; and acontroller configured or programmed to decrease a supply amount of thehydraulic fluid from the travel pump to the travel motor based on atravel state of the machine body when performing either one of aspeed-increase operation of switching the travel switching valve fromthe first state to the second state and a speed-decrease operation ofswitching the travel switching valve from the second state to the firststate, wherein when the speed-increase operation is performed, thecontroller switches the travel switching valve from the first state tothe second state in a prior period lasting up to when the supply amountto the travel motor starts decreasing, in a restoration period in whichthe supply amount to the travel motor after being decreased is beingrestored, or in an after-restoration period in which the supply amountto the travel motor has been restored.
 2. A working machine, comprising:a prime mover; a travel pump driven by power of the prime mover todeliver a hydraulic fluid; a travel motor rotated by the hydraulic fluiddelivered by the travel pump; a machine body where the prime mover, thetravel pump, and the travel motor are provided; a travel switching valveswitchable to a first state in which a rotation speed of the travelmotor is capable of being increased up to a first maximum speed, and toa second state in which the rotation speed of the travel motor iscapable of being increased up to a second maximum speed that is greaterthan the first maximum speed; a travel operation device including anoperation valve operable to change a pressure of a hydraulic fluid tooperate the travel pump in accordance with an operation of an operationmember; and a controller configured or programmed to decrease a supplyamount of the hydraulic fluid from the travel pump to the travel motorbased on a travel state of the machine body when performing either oneof a speed-increase operation of switching the travel switching valvefrom the first state to the second state and a speed-decrease operationof switching the travel switching valve from the second state to thefirst state, wherein when the speed-decrease operation is performed, thecontroller switches the travel switching valve from the second state tothe first state in a prior period lasting up to when the supply amountto the travel motor starts decreasing, in a decrease period in which thesupply amount to the travel motor is being decreased, or in anafter-restoration period in which the supply amount to the travel motorafter being decreased has been restored.
 3. The working machineaccording to claim 1, wherein when the speed-decrease operation isperformed, the controller switches the travel switching valve from thesecond state to the first state in the prior period lasting up to whenthe supply amount to the travel motor starts decreasing, in a decreaseperiod in which the supply amount to the travel motor is beingdecreased, or in the after-restoration period in which the supply amountof the travel motor after being decreased has been restored.
 4. Theworking machine according to claim 1, further comprising: a traveldetector to detect a travel speed of the machine body as the travelstate, wherein when the speed-increase operation is performed, thecontroller determines a decrease amount of the supply amount to thetravel motor corresponding to the travel speed detected by the traveldetector, and decreases the supply amount to the travel motor inaccordance with the decrease amount that has been determined.
 5. Theworking machine according to claim 2, further comprising: a traveldetector to detect a travel speed of the machine body as the travelstate, wherein when the speed-decrease operation is performed, thecontroller determines a decrease amount of the supply amount to thetravel motor corresponding to the travel speed detected by the traveldetector, and decreases the supply amount to the travel motor inaccordance with the decrease amount that has been determined.
 6. Theworking machine according to claim 1, further comprising: a switchoperable to issue a speed-change instruction of either increasing ordecreasing speed; and an accelerator operable to determine a rotationspeed of the prime mover, wherein the controller decreases the supplyamount of the hydraulic fluid from the travel pump to the travel motorby decreasing the rotation speed of the prime mover, and when thespeed-change instruction of increasing the speed is issued by operatingthe switch, the controller switches the travel switching valve from thefirst state to the second state in accordance with the speed-changeinstruction in a prior period lasting up to when the rotation speed ofthe prime mover starts decreasing, in a restoration period in which therotation speed of the prime mover after being decreased to a value lowerthan a target rotation speed that is the rotation speed of the primemover determined by operating the accelerator is being restored, or inan after-restoration period in which the rotation speed of the primemover has been restored.
 7. The working machine according to claim 2,further comprising: a switch operable to issue a speed-changeinstruction of either increasing or decreasing speed; and an acceleratoroperable to determine a rotation speed of the prime mover, wherein thecontroller decreases the supply amount of the hydraulic fluid from thetravel pump to the travel motor by decreasing the rotation speed of theprime mover, and when the speed-change instruction of decreasing thespeed is issued by operating the switch, the controller switches thetravel switching valve from the second state to the first state inaccordance with the speed-change instruction in a prior period lastingup to when the rotation speed of the prime mover starts decreasing, in adecrease period in which the rotation speed of the prime mover is beingdecreased to a value lower than a target rotation speed that is therotation speed of the prime mover determined by operating theaccelerator, or in an after-restoration period in which the rotationspeed of the prime mover after being decreased to the value has beenrestored.
 8. The working machine according to claim 6, wherein when thespeed-change instruction of decreasing the speed is issued by operatingthe switch, the controller switches the travel switching valve from thesecond state to the first state in accordance with the speed-changeinstruction in the prior period lasting up to when the rotation speed ofthe prime mover starts decreasing, in a decrease period in which therotation speed of the prime mover is being decreased to a value lowerthan the target rotation speed determined by operating the accelerator,or in the after-restoration period in which the rotation speed of theprime mover after being decreased to the value has been restored.
 9. Theworking machine according to claim 1, further comprising: a switchoperable to issue a speed-change instruction of either increasing ordecreasing speed; and an actuating valve connected to the operationvalve on an upstream side or a downstream side of the operation valveand operable to control a hydraulic fluid that flows in the operationvalve, wherein when the speed-change instruction of increasing the speedis issued by operating the switch, the controller switches the travelswitching valve from the first state to the second state in accordancewith the speed-change instruction in a prior period lasting up to whenan opening of the actuating valve starts decreasing, in a restorationperiod in which the opening of the actuating valve after being decreasedis being restored, or in an after-restoration period in which theopening of the actuating valve after being decreased has been restored.10. The working machine according to claim 2, further comprising: aswitch operable to issue a speed-change instruction of either increasingor decreasing speed; and an actuating valve connected to the operationvalve on an upstream side or a downstream side of the operation valveand operable to control a hydraulic fluid that flows in the operationvalve, wherein when the speed-change instruction of decreasing the speedis issued by operating the switch, the controller switches the travelswitching valve from the second state to the first state in accordancewith the speed-change instruction in a prior period lasting up to whenan opening of the actuating valve starts decreasing, in a decreaseperiod in which the opening of the actuating valve is being decreased,or in an after-restoration period in which the opening of the actuatingvalve after being decreased has been restored.
 11. The working machineaccording to claim 9, wherein when the speed-change instruction ofdecreasing the speed is issued by operating the switch, the controllerswitches the travel switching valve from the second state to the firststate in accordance with the speed-change instruction in the priorperiod lasting up to when the opening of the actuating valve startsdecreasing, in a decrease period in which the opening of the actuatingvalve is being decreased, or in the after-restoration period in whichthe opening of the actuating valve after being decreased has beenrestored.
 12. The working machine according to claim 3, furthercomprising: a switch operable to issue a speed-change instruction ofeither increasing or decreasing speed; an accelerator operable todetermine a rotation speed of the prime mover; and an actuating valveconnected to the operation valve on an upstream side or a downstreamside of the operation valve and operable to control a hydraulic fluidthat flows in the operation valve, wherein when the speed-changeinstruction of increasing the speed is issued by operating the switch,the controller switches the travel switching valve from the first stateto the second state in accordance with the speed-change instruction in aprior period lasting up to when an opening of the actuating valve startsdecreasing, in a restoration period in which the opening of theactuating valve after being decreased is being restored, or in anafter-restoration period in which the opening of the actuating valve hasbeen restored, and when the speed-change instruction of decreasing thespeed is issued by operating the switch, the controller switches thetravel switching valve from the second state to the first state inaccordance with the speed-change instruction in a prior period lastingup to when a rotation speed of the prime mover starts decreasing, in adecrease period in which the rotation speed of the prime mover is beingdecreased to a value lower than a target rotation speed that is therotation speed of the prime mover determined by operating theaccelerator, or in an after-restoration period in which the rotationspeed of the prime mover after being decreased to the value has beenrestored.
 13. The working machine according to claim 6, wherein theswitch is a switch to output the speed-change instruction to thecontroller.
 14. The working machine according to claim 1, wherein whenthe speed-increase operation is performed, the controller causes anabsolute value of a gradient of a supply amount to the operation valvein the restoration period to be smaller than that in a decrease periodin which the supply amount to the travel motor is being decreased. 15.The working machine according to claim 2, wherein when thespeed-decrease operation is performed, the controller causes an absolutevalue of a gradient of a supply amount to the operation valve in thedecrease period to be smaller than that in the restoration period. 16.The working machine according to claim 3, further comprising: a traveldetector to detect a travel speed of the machine body as the travelstate, wherein when the speed-increase operation is performed, thecontroller determines a decrease amount of the supply amount to thetravel motor corresponding to the travel speed detected by the traveldetector, and decreases the supply amount to the travel motor inaccordance with the decrease amount that has been determined.
 17. Theworking machine according to claim 3, further comprising: a traveldetector to detect a travel speed of the machine body as the travelstate, wherein when the speed-decrease operation is performed, thecontroller determines a decrease amount of the supply amount to thetravel motor corresponding to the travel speed detected by the traveldetector, and decreases the supply amount to the travel motor inaccordance with the decrease amount that has been determined.
 18. Theworking machine according to claim 3, further comprising: a switchoperable to issue a speed-change instruction of either increasing ordecreasing speed; and an accelerator operable to determine a rotationspeed of the prime mover, wherein the controller decreases the supplyamount of the hydraulic fluid from the travel pump to the travel motorby decreasing the rotation speed of the prime mover, and when thespeed-change instruction of increasing the speed is issued by operatingthe switch, the controller switches the travel switching valve from thefirst state to the second state in accordance with the speed-changeinstruction in a prior period lasting up to when the rotation speed ofthe prime mover starts decreasing, in a restoration period in which therotation speed of the prime mover after being decreased to a value lowerthan a target rotation speed that is the rotation speed of the primemover determined by operating the accelerator is being restored, or inan after-restoration period in which the rotation speed of the primemover has been restored.
 19. The working machine according to claim 3,further comprising: a switch operable to issue a speed-changeinstruction of either increasing or decreasing speed; and an acceleratoroperable to determine a rotation speed of the prime mover, wherein thecontroller decreases the supply amount of the hydraulic fluid from thetravel pump to the travel motor by decreasing the rotation speed of theprime mover, and when the speed-change instruction of decreasing thespeed is issued by operating the switch, the controller switches thetravel switching valve from the second state to the first state inaccordance with the speed-change instruction in a prior period lastingup to when the rotation speed of the prime mover starts decreasing, in adecrease period in which the rotation speed of the prime mover is beingdecreased to a value lower than a target rotation speed that is therotation speed of the prime mover determined by operating theaccelerator, or in an after-restoration period in which the rotationspeed of the prime mover after being decreased to the value has beenrestored.
 20. The working machine according to claim 3, furthercomprising: a switch operable to issue a speed-change instruction ofeither increasing or decreasing speed; and an actuating valve connectedto the operation valve on an upstream side or a downstream side of theoperation valve and operable to control a hydraulic fluid that flows inthe operation valve, wherein when the speed-change instruction ofincreasing the speed is issued by operating the switch, the controllerswitches the travel switching valve from the first state to the secondstate in accordance with the speed-change instruction in a prior periodlasting up to when an opening of the actuating valve starts decreasing,in a restoration period in which the opening of the actuating valveafter being decreased is being restored, or in an after-restorationperiod in which the opening of the actuating valve has been restored.